VNX - Performance Characteristics

How do I monitor system health > Performance Characteristics

Performance Characteristics

The Analyzer Performance characteristics apply to disks/RAID Groups, SPs, RAID group LUNs (non-pool

LUNs), metaLUNs, thin LUNs, thick LUNs (traditional LUNs in a pool), VNX Snapshot Mount Points, snapshot

sessions, asynchronous mirrors, and/or front-end ports as shown in the sections and tables that follow.

There are several categories of performance characteristics. The categories available to customers are Basic

(default) and Advanced. The Advanced category includes both Basic and Advanced characteristics. You can

change between the Basic and Advanced characteristic display by selecting Customize Charts and

checking or clearing the Advanced box in the General tab. The Basic and Advanced performance

characteristics are shown in separate tables for each item.

SP

The Storage Processor (SP) processes all I/Os within the storage system, host requests, management and

maintenance tasks, as well as operations related to replication or migration features.

In Unisphere Analyzer, the statistics for an SP are based on the I/O workload from its attached hosts.

Utilization and cache metrics, however, also reflect any internal processing that is occurring.

Basic Characteristics

Characteristic Description Comment

Utilization Describes the fraction of a certain observation

period that the system component is busy serving

incoming requests. An SP or disk that shows 100%

(or close to 100%) utilization is a system bottleneck

since an increase in the overall workload will not

affect the component throughput; the component

has reached its saturation point. Since a LUN is

considered busy if any of its disks is busy, LUN

utilization usually presents a pessimistic view. That

is, a high LUN utilization value does not necessarily

indicate that the LUN is approaching its maximum

capacity.

When the SP becomes the

bottleneck, the utilization will be

at or close to 100%. An increase

in workload will have no further

impact on the SP throughput, but

the I/O response time will start

increasing more aggressively.

Queue Length The average number of requests within a certain

time interval waiting to be served by the

component, including the one in service.

A queue length of zero (which is

average) indicates an idle

system. If three requests arrive

at an idle SP at the same time,

only one of them can be served

immediately; the other two must

wait in the queue, resulting in a

queue length of three.

Response Time

(ms)

The average time, in milliseconds, required for one

request to pass through a system component,

including its waiting time.

The higher the queue length for

the SP, the more requests are

waiting in its queue, thus

increasing the average response

time of a single request. For a

given workload, queue length

and response time are directly

proportional.

Total

Bandwidth

(MB/s)

The average amount of data in Mbytes that is

passed through a system component per second.

Total bandwidth includes both read and write

requests.

Larger requests usually result in

a higher total bandwidth than

smaller requests.

Total

Throughput

(IO/s)

The average number of requests that pass through

a system component per second. Total throughput

includes both read and write requests.

Since smaller requests need a

shorter time for this, they usually

result in a higher total

throughput than larger requests.

Read

Bandwidth

(MB/s)

The average number of Mbytes read that were

passed through a component per second.


a higher bandwidth than smaller

requests.

Read Size (KB) The average read request size in Kbytes. This number indicates whether

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Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)

the overall read workload is

oriented more toward throughput

(I/Os per second) or bandwidth

(Mbytes/second). For a finer

distinction of I/O sizes, use an IO

Size Distribution chart for the

LUNs.

Read

Throughput

(IO/s)

The average number of read requests passed

through a component per second.

Since smaller requests need less

processing time, they usually

result in a higher read


Write

Bandwidth

(MB/s)

The average number of Mbytes written that were




requests.

Write Size (KB) The average write request size in Kbytes. This number indicates whether

the overall write workload is






LUNs.

Write

Throughput

(IO/s)

The average number of write requests passed




result in a higher write


Service Time

(ms)

Time, in milliseconds, a request spent being

serviced by a component. It does not include time

waiting in a queue. Service time is mainly a

characteristic of the system component. However,

larger I/Os take longer and therefore usually result

in lower throughput (IO/s) but better bandwidth

(Mbytes/s).

Larger requests usually have a

longer service time than smaller

requests.


SP Cache Dirty

Pages (%)

Advanced Only

Percentage of cache pages owned

by this SP (pages committed to

cache, but not yet written to

disk). In an optimal environment,

the dirty-pages percentage will not exceed the high watermark

for a long period.

This metric shows the level of the write cache at

the last poll time and is not as an average over

the last polling interval.

SP Cache Flush

Ratio Advanced

Only

The fraction of the number of

flush operations performed

compared to the number of write

requests. Since the ratio is a

measure for the back-end activity

compared to front-end activity, a

lower number indicates better

performance.

A flush operation is a write of a portion of the

cache to make room for incoming write data.

SP Cache MBs

Flushed/ s

(MB/s) Advanced

Only

The number of megabytes per

second written from the write

cache to the disks.

The value is a measure of back-end activity.

SP Cache High

Water Flush On

Advanced Only

Number of times, since the last

sample, that the number of

modified pages in the write cache

reached the high watermark. The

higher the number, the greater

the write workload coming from

This number will only increase if the percentage of

Dirty Pages has previously reached the low

watermark.



Disk/RAID Group

As the slowest devices in a storage system, disk drives are very often responsible for performance-related

issues. Therefore, we recommend that you pay close attention to disk drives when analyzing performance

problems. RAID Group values are an aggregate of their disk performance values.


the host.

SP Cache Idle

Flush On

Advanced Only


sample, that the write cache

started flushing dirty pages to

disk due to a given idle period.

Idle flushes indicate a low

workload.

SP Cache Low

Water Flush Off

Advanced Only


sample, that the number of

modified pages in the write cache

reached the low watermark, at

which point the SP stops flushing

the cache. The higher the

number, the greater the write

workload coming from the host.

This number should be close to

the High Watermark Flush On

number.

This number will only increase if the percentage of

Dirty Pages has previously reached the high

watermark.

SP Write Cache

Flushes/s

Advanced Only

Number of times per second that

the write cache performed a flush

operation. A flush operation is a

write of a portion of a cache for

any reason; it includes forced

flushes, flushes resulting from

high watermark, and flushes from

an idle state. This value indicates

back-end workload.

A flush operation writes contiguous data out to

disk. This includes forced flushes, flushes resulting

from watermark processing, and flushes due to

idleness.

Average Busy

Queue Length

Advanced Only

Average number of requests

waiting at a busy system

component to be serviced,

including the request that is

currently in service.

Since this queue length is counted only when the

SP is not idle, the value indicates the frequency

variation (burst frequency) of incoming requests.

The higher the value, the bigger the burst and the

longer the average response time at this

component. In contrast to this metric, the

average queue length does also include idle

periods when no requests are pending. If you

have 50% of the time just one outstanding

request, and the other 50% the SP is idle, the

average busy queue length will be 1. The average

queue length however, will be .

FAST Cache Dirty

Pages (%)

Advanced Only

Percentage of FAST Cache pages

owned by this SP that contain

data, which has not yet been

written back to disks.

This metric shows the instantaneous level of the

FAST Cache based on the last poll. It is not an

average over the entire polling interval.

FAST Cache MBs

Flushed (MB/s)

Advanced Only

Number of megabytes per second

that have been written from the

FAST Cache back to disks.

N/A


Utilization Describes the fraction of a certain observation period

that the system component is busy serving incoming

requests. An SP or disk that shows 100% (or close to

100%) utilization is a system bottleneck since an

increase in the overall workload will not affect the

component throughput; the component has reached

its saturation point. Since a LUN is considered busy if

any of its disks is busy, LUN utilization usually

Since a RAID group can have

multiple partitions, the disks

utilization is a result of servicing

I/Os that belong to all LUNs

within this RAID group.



presents a pessimistic view. That is, a high LUN

utilization value does not necessarily indicate that the

LUN is approaching its maximum capacity.

Queue Length The average number of requests within a certain time

interval waiting to be served by the component,

including the one in service.


average) indicates an idle disk.

If three requests arrive at an

idle disk at the same time, only

one of them can be served

immediately; the other two

must wait in the queue,

resulting in a queue length of

three.

Response Time

(ms)





the disk, the more requests are






proportional.

Total Bandwidth

(MB/s)

The average amount of data in Mbytes that is passed

through a system component per second. Total

bandwidth includes both read and write requests.

Larger requests result usually in


smaller requests.

Total

Throughput

(IO/s)

The average number of requests that pass through a

system component per second. Total throughput


Since smaller requests need

less processing time, they

usually result in a higher total

throughput than larger

requests.

Read Bandwidth

(MB/s)





ones.


the read workload is oriented

more toward throughput (I/Os

per second) or bandwidth


distinction of I/O sizes, use an

IO Size Distribution chart.

Read

Throughput

(IO/s)

The average number of read requests passed through

a component per second.



usually result in a higher write


requests.

Write

Bandwidth

(MB/s)





ones.

Write Size (KB) The average write request size in Kbytes. This

number indicates whether the read workload is

oriented more toward throughput (I/Os per second)

or bandwidth (Mbytes/second). For a finer distinction

of I/O sizes, use an IO Size Distribution chart.

Sequential writes can get

coalesced in the write cache and

might result in larger disk

requests when flushed to disks.

Write

Throughput

(IO/s)





usually result in a higher write


requests.

Average Seek

Distance (GB)

Average seek distance in gigabytes. Longer seek distances result in

longer seek times and therefore

higher response times.

Defragmentation might help to

reduce seek distances.




LUN

A LUN is an abstract object whose performance depends on various factors. The main aspect is whether a

host I/O can get satisfied by the cache or not. A cache hit does not require any disk access; a cache miss

however requires one or more disk accesses to complete the data request. Most cache statistics are

available only for the LUN object.

Unisphere Analyzer reports performance statistics for the following types of LUNs: regular host LUNs,

metaLUNs, thin LUNs, thick pool LUNs, and component LUNs, which are the underlying LUNs of a metaLUN.


Service Time

(ms)

Time, in milliseconds, a request spent being serviced

by a component. It does not include time waiting in a

queue. Service time is mainly a characteristic of the

system component. However, larger I/Os take longer

and therefore usually result in lower throughput

(IO/s) but better bandwidth (Mbytes/s).

If there are at least three

outstanding requests to the

disk, it will optimize the order of

execution based on their locality

which can result in a shorter

service time.


Average Busy

Queue Length

Advanced Only

Average number of

requests waiting at a

busy system

component to be

serviced, including the

request that is


Since this queue length is counted only when the disk is not

idle, the value indicates the frequency variation (burst

frequency) of incoming requests. The higher the value, the

bigger the burst and the longer the average response time at

this component. In contrast to this metric, the average queue

length does also include idle periods when no requests are

pending. If you have 50% of the time just one outstanding

request, and the other 50% the disk is idle, the average busy

queue length will be 1. The average queue length however,

will be .

Average Seek

Distance (GB)

Advanced Only

Average seek distance

in gigabytes.

Longer seek distances result in longer seek times and

therefore higher response times. Defragmentation might help

to reduce seek distances.



period that the system component is busy

serving incoming requests. An SP or disk that

shows 100% (or close to 100%) utilization is a

system bottleneck since an increase in the

overall workload will not affect the component

throughput; the component has reached its

saturation point. Since a LUN is considered busy

if any of its disks is busy, LUN utilization usually

presents a pessimistic view. That is, a high LUN

utilization value does not necessarily indicate

that the LUN is approaching its maximum

capacity.

When the LUN becomes the

bottleneck, the utilization will be at

or close to 100%. However, since

I/Os can get serviced by multiple

disks an increase in workload might

still result in a higher throughput.





average) indicates an idle LUN.

Since there can be idle times during

the observed time period, the

average queue length can also be

smaller than 1. If you want to know

the average number of outstanding

requests when the LUN is busy, look

at the average busy queue length.

Response Time

(ms)

The average time, in milliseconds, required for

one request to pass through a system

component, including its waiting time.

The higher the queue length for a

LUN, the more requests are waiting

in its queue, thus increasing the

average response time of a single

request. For a given workload,

queue length and response time are




directly proportional.

Total

Bandwidth

(MB/s)




requests.

Larger requests usually result in a

higher total bandwidth than smaller

requests.

Total

Throughput

(IO/s)

The average number of requests that pass

through a system component per second. Total

throughput includes both read and write

requests.



result in a higher total throughput

than larger requests.

Read

Bandwidth

(MB/s)




higher bandwidth than smaller

requests.

Read Size (KB) The average read request size in Kbytes. This number indicates whether the

overall read workload is oriented

more toward throughput (I/Os per

second) or bandwidth



Size Distribution chart for this LUN.

Read

Throughput

(IO/s)




processing time, they usually result

in a higher read throughput than

larger requests.

Write

Bandwidth

(MB/s)




higher bandwidth than smaller

requests.

Write Size (KB) The average write request size in Kbytes. This number indicates whether the

overall write workload is oriented

more toward throughput (I/Os per

second) or bandwidth



Size Distribution chart for the LUNs.

Write

Throughput

(IO/s)




processing time, they usually result

in a higher write throughput than

larger requests.

Service Time

(ms)


serviced by a component. It does not include

time waiting in a queue. Service time is mainly a

characteristic of the system component.

However, larger I/Os take longer and therefore

usually result in lower throughput (IO/s) but

better bandwidth (Mbytes/s).



requests.


Full Stripe

Writes/s

Advanced

Average number of writes

requests per second that spanned

a whole stripe (all disks in a LUN).

This metric is applicable only to LUNs that are part

of a RAID 5 or RAID 3 Group. For these RAID

types, full stripe writes are most efficient since

data and parity can be written out to the disks

without having to pre-read any old data or parity

first.

Prefetch

Bandwidth

(MB/s)

The amount of data per second

that has been prefetched for this

particular LUN.

The amount of prefetched data depends on the

prefetch settings for this LUN. It indicates the

sequentiality of the workload for this LUN.

Used Prefetches

(%) Advanced

The indication of prefetching

efficiency.

To improve read bandwidth, two consecutive

requests trigger prefetching, thereby filling the



Only read cache with data before it is requested. Thus,

sequential requests will receive the data from the

read cache instead of from the disks, which

results in a lower response time and higher

throughput. As the percentage of sequential

requests rises, so does the percentage of used

prefetches.

SP Cache Read

Hits/s Advanced

Only

The number of read requests that

were satisfied by either write or

read cache within a second.

An SP read cache hit occurs when recently

accessed data is re-referenced while it is still in

the cache.

SP Cache Read

Misses/s

Advanced Only

The rate of read requests that

could not be satisfied by the SP

cache and therefore required a

disk access.

SP Cache Reads

From WC/s

Average number of read requests

per second that were satisfied by

the write cache only.

Reads from write cache occur when recently

written data is read again while it is still in the

write cache. This is a subset of SP cache read hits

which includes requests satisfied by either the

write or the read cache.

SP Cache Reads

From RC/s



the read cache only.

Reads from read cache occur when data that has

been recently read or prefetched is re-read while

it is still in the read cache. This is a subset of SP

cache read hits which includes requests satisfied

by either the write or the read cache.

SP Cache Read

Hit Ratio

Advanced Only

The fraction of read requests

served from both read and write

caches vs. the number of read

requests to this LUN.

A higher ratio indicates better read performance.

SP Cache Write

Rehits/s

Advanced Only

The number of write requests per

second that were satisfied by the

write cache since they have been

referenced before and not yet

flushed to the disks.

SP cache write rehits occur when recently

accessed data is referenced again while it is still in

the write cache. This is a subset of SP Cache

Write Hits.

SP Cache Write

Hit Ratio

Advanced Only

The fraction of write requests that

were satisfied by the write cache

without requiring any disk access,

compared to the total number of

write requests to this LUN.

A higher ratio indicates better write performance.

SP Cache Write

Rehit Ratio

Advanced Only



since they have been referenced

before and not yet flushed to the

disks, compared to the total

number of write requests to this

LUN.

This is a measure of how often the write cache

succeeded in eliminating a write operation to disk.

While improving the rehit ratio is useful it is more

beneficial to reduce the number of forced flushes.

SP Cache Write

Hits/s Advanced

Only

The number of write requests that


without requiring any disk access.

SP cache write hits are either

requests that have been


flushed to the disks (rehits) or

new write requests that did not

trigger any forced flushes.

Write requests that are not SP cache write hits are

referred to as SP cache write misses.

SP Cache Write

Misses/s

Advanced Only


second that could not be satisfied

by the write cache only, but also

required additional disk access.

Examples of SP cache write misses are write

requests that bypass the write cache due to their

size and write requests that trigger forced flushes.

SP Cache Forced

Flushes/ s

Advanced Only

Number of times per second the

cache had to flush pages to disk

to free space for incoming write

SP cache forced flushes are a measure of how

often write requests will have to wait for disk I/O

rather than be satisfied by an empty slot in the



requests. SP cache forced flushes

indicate that the incoming

workload is higher than the back

end workload. A relatively high

number over a long period of time

suggests that you spread the load

over more disks.

write cache. In most well performing systems this

should be zero most of the time.

Disk Crossing

(%) Advanced

Only Percentage of requests that

require I/O to at least two disks


server requests.

A single disk crossing can involve more than two

disk drives; that is, more than two stripe element

crossings. Disk crossings relate to the LUN stripe

element size. Generally, a low value is needed for

good performance.

Average Busy

Queue Length

Advanced Only







LUN is not idle, the value indicates the frequency







have 50%of the time just one outstanding

request, and the other 50% the LUN is idle, the



Explicit Trespass

Count

The result of an external

command that you or the failover

software issue. When an SP

receives this command (from the

failover software or you issuing

the LUN trespass in Unisphere),

LUN ownership is transferred to

that SP.

This host-side performance characteristic is

displayed in both archive dump files and charts

(runtime and archive).

Implicit Trespass

Count

The result of software controls

within the storage system. An

example of an implicit trespass

operation is when LUN ownership

is transferred to the SP (non-

optimal paths) that receives the

heaviest I/O activity. Once a

threshold of I/Os is reached on

the non-optimal paths, the

CLARiiON implicitly trespasses the

LUN to that SP.

This host-side performance characteristic is

displayed in both archive dump files and charts

(runtime and archive).

FAST Cache

Read Hit/s

Advanced Only


per second for this LUN that were

satisfied by FAST Cache.

A FAST Cache read hit occurs when data is read,

which is currently present in FAST Cache. This

includes data that has been flushed already, but

not yet invalidated in the FAST Cache.

FAST Cache

Read Misses/s

Advanced Only



not satisfied by FAST Cache.

A FAST Cache read miss does not necessarily

require disk access. It still might get satisfied by

the SP cache.

FAST Cache

Read Hit Ratio

Advanced Only

The fraction of all read requests

for this LUN that have been


Valid numbers are between 0 and 1.

FAST Cache

Write Hits/s

Advanced Only

Average number of write requests



Write requests that are not write cache hits are

referred to as write cache misses.

FAST Cache

Write Misses/s

Advanced Only



not satisfied by FAST Cache.

A FAST Cache write miss does not necessarily

require a disk access. It still might get satisfied by

the SP cache.

FAST Cache

Write Hit Ratio

The fraction of all write requests

for this LUN that have been

N/A



Optimal and Nonoptimal Characteristics (Advanced-only)

You will see the Optimal and Nonoptimal performance characteristics only if you enable the advanced mode

in the Customize dialog box and are running the active/active feature. Optimal refers to the path that is

ready to do I/O and will yield the best performance. Nonoptimal refers to the path that is ready to do I/O,

but may not yield the best performance. The following Optimal and Nonoptimal performance characteristics

apply to LUN objects:

Advanced-only Characteristics

MetaLUNs

Unisphere Analyzer reports the following performance statistics for metaLUNs:


Advanced Only satisfied by FAST Cache.

Optimal

Performance

Characteristic

Nonoptimal

Performance

Characteristic

Utilization-Optimal [%] Utilization-Nonoptimal [%]

Queue Length-Optimal Queue Length-Nonoptimal

Response Time-Optimal Response Time-Nonoptimal

Total Bandwidth-Optimal [MB/s] Total Bandwidth-Nonoptimal [MB/s]

Total Throughput-Optimal [IO/s] Total Throughput-Nonoptimal [IO/s

Read Bandwidth-Optimal [MB/s] Read Bandwidth-Nonoptimal [MB/s]

Read Size-Optimal [KB] Read Size-Nonoptimal [KB]

Read Throughput-Optimal [IO/s] Read Throughput-Nonoptimal [IO/s]

Write Bandwidth-Optimal [MB/s] Write Bandwidth-Nonoptimal [MB/s]

Write Size-Optimal [KB] Write Size-Nonoptimal [KB]

Write Throughput-Optimal [IO/s] Write Throughput-Nonoptimal [IO/s]

Average Busy Queue Length-Optimal Average Busy Queue Length-Nonoptimal

Service Time-Optimal [ms] Service Time-Nonoptimal [ms]

Explicit Trespass Count-Optimal Explicit Trespass Count-Nonoptimal

Implicit Trespass Count-Optimal Implicit Trespass Count-Nonoptimal













capacity.

When the SP becomes the





















Response Time

(ms)











proportional.

Total

Bandwidth

(MB/s)




requests.



smaller requests.

Total

Throughput

(IO/s)








Read

Bandwidth

(MB/s)





requests.








LUNs.

Read

Throughput

(IO/s)







Write

Bandwidth

(MB/s)





requests.








LUNs.

Write

Throughput

(IO/s)







Service Time

(ms)







(Mbytes/s).



requests.


Full Stripe

Writes/s

Average number of writes

requests per second that spanned

This metric is applicable only to LUNs that are part

of a RAID 5 or RAID 3 Group. For these RAID



Advanced a whole stripe (all disks in a LUN). types, full stripe writes are most efficient since

data and parity can be written out to the disks

without having to pre-read any old data or parity

first.

Used Prefetches

(%) Advanced

Only

The indication of prefetching

efficiency.

To improve read bandwidth, two consecutive

requests trigger prefetching, thereby filling the

read cache with data before it is requested. Thus,

sequential requests will receive the data from the

read cache instead of from the disks, which

results in a lower response time and higher

throughput. As the percentage of sequential

requests rises, so does the percentage of used

prefetches.

SP Cache Read

Hits/s Advanced

Only

The number of read requests that

were satisfied by either write or

read cache within a second.

An SP cache read hit occurs when recently

accessed data is re-referenced while it is still in

the cache.

SP Cache Read

Misses/s

Advanced Only

The rate of read requests that

could not be satisfied by the SP

cache and therefore required a

disk access.

SP Cache Reads

From WC/s



the write cache only.

SP cache reads from write occur when recently

written data is read again while it is still in the

write cache. This is a subset of SP cache read hits

which includes requests satisfied by either the

write or the read cache.

SP Cache Reads

From RC/s



the read cache only.

SP cache reads from read occur when data that

has been recently read or prefetched is re-read

while it is still in the read cache. This is a subset

of SP cache read hits, which includes requests

satisfied by either the write or the read cache.

SP Cache Read

Hit Ratio

Advanced Only

The fraction of read requests

served from both read and write

caches vs. the number of read

requests to this LUN.

A higher ratio indicates better read performance.

SP Cache Write

Rehits/s

Advanced Only


second that were satisfied by the

write cache since they have been


flushed to the disks.

Write cache rehits occur when recently accessed

data is referenced again while it is still in the write

cache. This is a subset of Write Cache Hits.

SP Cache Write

Hit Ratio

Advanced Only



without requiring any disk access,


write requests to this LUN.

A higher ratio indicates better write performance.

SP Cache Write

Rehit Ratio

Advanced Only



since they have been referenced

before and not yet flushed to the

disks, compared to the total

number of write requests to this

LUN.

This is a measure of how often the write cache

succeeded in eliminating a write operation to disk.

While improving the rehit ratio is useful it is more

beneficial to reduce the number of forced flushes.

SP Cache Write

Hits/s Advanced

Only

The number of write requests that


without requiring any disk access.

SP cache write hits are either

requests that have been


flushed to the disks (rehits) or

new write requests that did not

trigger any forced flushes.



SP Cache Write The number of write requests per Write requests that cause forced flushes or that



Misses/s

Advanced Only

second that could not be satisfied

by the write cache only, but also

required additional disk access.

Examples of SP cache write

misses are write requests that

bypass the write cache due to

their size and write requests that

trigger forced flushes.

bypass the write cache due to their size are

examples of SP cache write misses.

SP Cache Forced

Flushes/s

Advanced Only

Number of times per second the

cache had to flush pages to disk

to free space for incoming write

requests. SP cache forced flushes

indicate that the incoming

workload is higher than the back

end workload. A relatively high

number over a long period of time

suggests that you spread the load

over more disks.

SP cache forced flushes are a measure of how

often write requests will have to wait for disk I/O

rather than be satisfied by an empty slot in the

write cache. In most well performing systems this

should be zero most of the time.

Disk Crossing

(%) Advanced

Only Percentage of requests that

require I/O to at least two disks


server requests.

A single disk crossing can involve more than two

disk drives; that is, more than two stripe element

crossings. Disk crossings relate to the LUN stripe

element size. Generally, a low value is needed for

good performance.

Average Busy

Queue Length

Advanced Only







LUN is not idle, the value indicates the frequency







have 50%of the time just one outstanding

request, and the other 50% the LUN is idle, the



LUN Read

Crossings/s

Advanced Only

The number of LUN crossings per

second that a read request to a

MetaLUN caused.

Since metaLUNs consist of multiple LUNs, a single

read request can access disk drives that belong to

two or more of these conventional LUNs.

LUN Write

Crossings/s

Advanced Only

The number of LUN crossings per

second that a write request to a

metaLUN caused.

Since metaLUNs consist of multiple LUNs, a single

write request can access disk drives that belong

to two or more of these conventional LUNs.

Explicit Trespass

Count

The result of an external

command that you or the failover

software issues. When an SP

receives this command (from the

failover software or you issuing

the LUN trespass in Unisphere),

LUN ownership is transferred to

that SP.

Host-side performance characteristic displayed in

both archive dump files and charts (runtime and

archive).

Implicit Trespass

Count

The result of software controls

within the storage system. An

example of an implicit trespass

operation is when LUN ownership

is transferred to the SP (non-

optimal paths) that receives the

heaviest I/O activity. Once a

threshold of I/Os is reached on

the non-optimal paths, the

CLARiiON implicitly trespasses the

LUN to that SP.

Host-side performance characteristic displayed in

both archive dump files and charts (runtime and

archive).

FAST Cache

Read Hit/s

Advanced Only


per second for this metaLUN that

were satisfied by FAST Cache.











apply to MetaLUN objects:


Thin LUNs

Unisphere Analyzer reports the following performance statistics for thin LUNs:



FAST Cache

Read Misses/s

Advanced Only



were not satisfied by FAST Cache.


require disk access. It still might get satisfied by

the SP cache.

FAST Cache

Read Hit Ratio

Advanced Only

The fraction of all read requests

for this metaLUN that have been



FAST Cache

Write Hits/s

Advanced Only



were satisfied by FAST Cache.



FAST Cache

Write Misses/s

Advanced Only



were not satisfied by FAST Cache.


require a disk access. It still might get satisfied by

the SP cache.

FAST Cache

Write Hit Ratio

Advanced Only

The fraction of all write requests

for this metaLUN that have been


N/A

Optimal

Performance

Characteristic

Nonoptimal

Performance

Characteristic














Explicit Trespass Count-Optimal Explicit Trespass Count-Nonoptimal

Implicit Trespass Count-Optimal Implicit Trespass Count-Nonoptimal


Utilization Describes the fraction of a certain observation When the SP becomes the













capacity.


















Response Time

(ms)











proportional.

Total

Bandwidth

(MB/s)




requests.



smaller requests.

Total

Throughput

(IO/s)








Read

Bandwidth

(MB/s)





requests.








LUNs.

Read

Throughput

(IO/s)







Write

Bandwidth

(MB/s)





requests.








LUNs.









apply to thin LUN objects:


Pools

Unisphere Analyzer reports the following performance statistics for pools:


Write

Throughput

(IO/s)







Service Time

(ms)







(Mbytes/s).

Since thin LUNs consist of

multiple LUNs, a single read

request can access disk drives

that belong to two or more of

these conventional LUNs.


Average Busy

Queue Length

Advanced Only

Average number of

requests waiting at a

busy system

component to be

serviced, including the

request that is


Since this queue length is counted only when the LUN is not

idle, the value indicates the frequency variation (burst

frequency) of incoming requests. The higher the value, the

bigger the burst and the longer the average response time

at this component. In contrast to this metric, the average

queue length does also include idle periods when no

requests are pending. If you have 50%of the time just one

outstanding request, and the other 50% the LUN is idle, the

average busy queue length will be 1. The average queue

length however, will be .

Optimal

Performance

Characteristic

Nonoptimal

Performance

Characteristic
















MirrorView/A

When using the optional replication software, Mirrorview/A (asynchronous mirroring), changed data is

copied from a primary image, the source LUN, to a secondary image. These updates can be invoked either

automatically or manually. Either way, there will be times when primary and secondary image are different,

that is, out of sync. Unisphere Analyzer provides performance statistics regarding the data transfer and the

difference between the primary and secondary images for each Remote Mirror.



FAST Cache Read

Hits/s Advanced Only

Average number of read

requests per second for this

pool that were satisfied by

FAST Cache.





FAST Cache Read

Misses/s Advanced

Only

Average number of read


pool that were not satisfied by

FAST Cache.


require a disk access. It still might get statisfied

by the SP cache.

FAST Cache Read Hit

Ratio Advanced Only

The fraction of all read

requests for this pool that have

been satisfied by FAST Cache.


FAST Cache Read

Write Hits/s

Advanced Only

Average number of write


pool that were satisfied by

FAST Cache.

Write requests that are not write cache hits are

referred to as write cache misses.

FAST Cache Write

Misses/s Advanced

Only

Average number of write


pool that were not satisfied by

FAST Cache.


require a disk access. It still might get satisfied

by the SP cache.

FAST Cache Write Hit

Ratio Advanced Only

The fraction of all write

requests for this LUN that have

been satisfied by FAST Cache.

N/A


Total Bandwidth

(MB/s)

Bandwidth of the update

transfers from the

primary image to the

secondary image(s).

Total Throughput

(IO/s)

Throughput of the update

transfers from the


secondary image(s).

Average Transfer

Size (KB)

Average size of update

transfers from the


secondary image(s).

Time Lag (min) The measure of how far,

in time, the secondary

image is behind the

primary image(s).

This is the time that has passed since the last update

successfully finished.

Megabyte Lag

(MB)

The number of

megabytes by which the

secondary image differs

from the primary image

(s).

This number indicates how much data has to be written to

the secondary image to make both, primary and

secondary image in-sync. During an update, this value is a

combination of how much data is remaining to be sent plus

any newly updated data that will be part of the following

update.

Cycle Count The number of updates

that completed during the

polling interval.

An update that started but did not finish within the same

polling interval will not be counted. This number will be

greater than one only if the time between polls is fairly



SnapSession

The snapshot characteristics apply to a Snapshot Session node only (SnapView software required). In the

Snapshot Session, these characteristics are shown as SS.

SnapSessions are available with the optional software package, SnapView. During a SnapSession, data that

a production host overwrites on a source LUN will be saved in the SnapCache (part of the Reserved LUN

Pool), thus preserving a point-in-time view of this LUN from the time the SnapSession was created (Start

Session). This view can then get exported to another host (Activate Session) that needs to access this data.

The following table contains all statistics that Unisphere Analyzer provides for a SnapSession. Since a

SnapSession can contain multiple SnapShot Source LUNs, the statistics comprise all LUNs that are

associated with this SnapSession.



Ports

Unisphere Analyzer reports performance statistics for front-end ports.


large.

Average Cycle

Time (min)

The average duration of

all updates that finished

within the polling

interval..

If only a single update finished within the polling interval

(Cycle Count = 1), this time indicates the duration of this

update. For multiple update completions (Cycle Count >

1), this value will return their average duration.


Reads From

Snapshot LUN

The number of read requests on

snapshots during this snapshot session.

These are requests that originate for

instance from a backup host and read data

either from the source LUN or the

SnapCache.

Reads From

Snapshot Source

LUN

The number of reads during this

Snapshot session from the source LUN.

It is calculated by the difference

between Total Reads in Session and

Reads From Cache.

These are read requests that originate from

a backup host and access data that has not

been overwritten since the SnapSession

started and therefore are satisfied by the

Source LUN.

Writes To

Snapshot Source

LUN

The number of writes during this

Snapshot session to the source LUN (on

the pertinent SP).


Reads From

Snapshot Cache

Advanced Only

The number of reads during this

session that have resulted in a

read from the Snapshot cache

(instead of a read from the source

LUN).

These are read requests that originate from a

backup host and access data that has been

previously overwritten on the source LUN

during this SnapSession and therefore are

satisfied by one or more Snap Cache LUNs.

Writes To Snapshot

Cache Advanced Only

The number of writes to the

source LUN this session that

triggered a copy-on-write

operation (the first write to each

snapshot cache chunk region).

Write requests that trigger multiple copy-on-

first-write operations due to misalignment or

their size will only be counted once.

Writes Larger Than

Cache Chunk Size

Advanced Only

The number of writes to the

source LUN during this session

that were larger than the chunk

size (they have resulted in

multiple writes to the cache).

These writes result in multiple copy-on-first-

write operations.

Chunks Used in

Snapshot Copy

Session Advanced

Only

The number of snapshot cache

chunks that this session has used.



Highlight a performance metric

Expand and Collapse

Select or Highlight

Checkbox

IO Size Distribution Detail chart

IO Size Distribution Summary Chart

LUN IO Disk Detail chart

Performance Detail chart

Performance Overview window

Performance Summary chart

Performance Survey chart

Data Logging

Customize dialog box - General

Customize dialog - Archives

Customize dialog - Fonts

Customize dialog - Line Charts

Customize dialog - Summary Charts

Customize dialog - Survey Charts

Customize dialog - Warnings

Control Panel - Policies tab

Policy Builder

Object states

Operational states

Display an archive file

Display a real-time chart

Customize Analyzer displays

Retrieve Performance Data and Store it in an Archive File

Configure a Performance Detail chart

Display a Performance Detail chart

Display a Performance Summary chart

Display a Performance Survey chart

Display an IO Size Distribution chart

Display a LUN IO Disk Detail chart

Display storage system performance information

Dump archive files into text format


Queue Full

Count

The number of Queue Full events

that occurred for a particular

front-end port during a polling

interval.

A Queue Full response is sent to the host when the

port receives more requests than it can accept at

once. This event should never occur in a properly

configured SAN environment.

Related references

Related tasks



Create a policy

Destroy a policy

Measure a policy

Modify a policy

Run a policy

Stop the current policy

About Unisphere Analyzer

Analyzer dependencies

Analyzer charts (real time and archive file)

Workload characteristics

Use Analyzer to monitor cache performance

About policies

Work with the Policy Builder wizard

Related concepts



Documents

VNX - Performance Characteristics