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Technology Brief: MAXio® All Flash Array

The Need for Extreme Write Speed

Write speed is critical to judge a storage system's performance. Not all

applications need extreme write speed, but for those that do, SSD technology is the

best solution. All flash arrays (AFAs) are comprised of SSDs and considered the fastest

storage system available. The centralized, high-speed systems are connected to either

single or multiple application servers or hyper-scale architectures. When connected

over iSCSI or Fiber Channel (FC), the AFA will outperform 20 internal server SAS drives

by up to 100x. However, not all AFAs are created equal.

The biggest challenge storage system manufacturers have is to figure out how

to harness the speed of SSDs for their all flash arrays. Historically, many manufacturers

have taken a quick-to-market route by using existing hard disk drive (HDD) RAID

controllers and algorithms and making several changes to accommodate SSDs. The

problem is that HDD RAID controllers and algorithms are not designed for SSDs,

instead used to manage devices with a much lower I/O range, usually around 100 to

400 IOPs. Hard disk drive controllers and algorithms constrict the overall performance

of SSDs and often shorten their lifespan by not completing tasks such as wear leveling.

All flash arrays, sometimes called Solid State Appliances (SSAs), belong to a

new class of enterprise storage systems consisting entirely of solid state drives (SSDs).

In contrast to traditional hard disk drives that typically handle hundreds of random I/O

requests per second, SSDs are able to handle tens of thousands of random I/Os per

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second. Solid state drives are also more energy-efficient, consuming only one-half to

one-third of power compared to HDDs. They have extremely low latency and can

manage close to 100 times more I/Os per second, greatly improving operational

efficiency by transacting more client requests in a fraction of the time. The traditional

RAID technologies designed for HDDs cannot take advantage of the SSDs. New

technology must be developed: FlexiRemap™.

Solid State Drives and Flash Memory

Before reviewing the FlexiRemap technology in detail, it helps to understand how

flash memory works. Flash memory is an electronic, nonvolatile storage medium

capable of being electrically erased and reprogrammed. Flash consists of blocks, with

each block breaking down into pages on which data is writable. Unlike HDDs, flash that

has pages with original data cannot be directly overwritten with newer, updated data.

The original data must first be copied to a new location. Once this operation is

complete, the data in the original location can be erased and replaced with the updated

data. For example, imagine you had a file entitled ‘ABC’ written on pages 001 through

003. An SSD would have to copy the data on pages 001 through 003 to a new location

before being able to save a new version of the file. The need to copy old data to a new

location greatly degrades system performance.

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Deploying FlexiRemap Technology

FlexiRemap technology is a flash-oriented software. It features an architectural

design tailored for the internal flash level workings of SSDs. FlexiRemap re-orders and

optimizes write I/Os in real-time before passing them to the underlying flash on the

SSDs. By intelligently reordering and re-mapping where write I/Os get placed,

FlexiRemap greatly improves performance of SSDs and prolongs the life of the flash.

Plus, with data redundancy built-in, FlexiRemap provides the most desirable benefits of

RAID.

To accelerate random writes, FlexiRemap deploys an innovative new technology

that aligns all writes into a string and then maps them to empty sequential block

addresses. Updated data writes do not need storage at the original location; all updated

data writes get placed at new, sequential locations. FlexiRemap technology makes write

performance much faster than most other all flash arrays. In the background,

FlexiRemap garbage collection will reclaim the old data locations and covert them to

fresh, empty spaces for new writes.

FlexiRemap RAID Maintains Performance During Drive Rebuild

The concept of RAID was developed to safeguard a failing drive. If a drive were

to fail, it could be replaced with a new one. This new drive would already need to have

the necessary data rebuilt before it can enter the existing RAID set. In most RAID

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algorithms, rebuilding data to a new drive (HDD or SDD) is very resource-intensive and

greatly degrades system performance.

To maintain performance during a drive rebuild, FlexiRemap divides the MAXio

All Flash Array SSDs into two groups: Group A designates drives 1 through 10 and

Group B designates drives 11 through 20. The group that includes the drive being

rebuilt will not accept any new writes. This will allow that group to devote all its SSD

resources to rebuilding the new drive. The other group will then accept new writes so

the system can maintain its write performance. Both groups will continue to respond to

read requests, as they need fewer resources.

The SSD Lifespan and Improved Performance

Unlike HDDs, SSDs have a finite number of re-write cycles known as Program-

Erase (P/E) cycles. Frequent programming to the same SSD will often lead to bad

blocks that shorten the lifespan of the device. The FlexiRemap global wear leveling

algorithm guarantees that data is evenly distributed across each SSD in the array.

FlexiRemap monitors the mapping table record to make sure that each SSD stores a

similar amount of data. When new data writes to the array, the drives with the lowest

P/E cycle count gets used. The benefit of evenly distributing data across all SSDs in an

array is that you extend the SSD lifespan.

Another benefit of evenly distributing data is better performance. Since every

SSD stores a similar amount of data, there is a lessened chance of traffic bottlenecks.

As noted below, test results show differences of about 1.5 times the number of requests

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received between the most-used and least-used SSD in a RAID system. With

FlexiRemap, each SSD is given a similar number of requests.

Conclusion

FlexiRemap technology is flash-oriented software. It features an architectural design

tailored for the fundamentals and internal flash level workings of SSDs. FlexiRemap

reorders and optimizes write I/Os in real time before passing them to the underlying

flash on the SSDs. By intelligently re-ordering and mapping where write I/Os get placed,

FlexiRemap greatly improves performance of SSDs and prolongs the life of the flash.

Plus, with data redundancy built in, FlexiRemap provides the most desirable benefits of

RAID without the limitations. FlexiRemap is at the core of the MAXio All Flash Array,

making it one of the fastest and cost effective AFAs in the industry