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TAPE ROTATIONSCHEME
Presentation By : S.A Adewale OloyiDate : April 2015
TAPES A tape is a storage device where information
is stored on. It’s an arguably better option to disk.
Why? Life cycleDurability
Ease of UseReliability
Disadvantage Speed !!!
Uncertainty of data integrityShoe-Shinning Effect
Types Of Tapes
Tape Data Cartridge
Tape Cleaning Cartridge
HP MSL 8096
HP MSL 4048
HP MSL2024
Tape Library
Tape Library
IBM Tape Library
Dell PowerVault TL4000
Tape Library
Dell PowerVault
TL2000
Tape Backup Technology
LTO3 LTO4 LTO5 LTO6
Linear Tape-Open (or LTO)
Tape Management Tapes have a long life cycle and durability nonetheless, they should still be managed appropriately for the sake of its contents- Hence, an effective management policyHow?By rotating the tapes
Tape Rotation Strategy Things to consider R.P.O (Recovery point Objective) Number of Tapes Available Off-site Storage Retention
StrategiesFor this presentation, 3 strategies will be discussed. G.F.S (Grandfather- Father- Son) Tower of Hanoi Round Robin
G.F.S Tape Rotation Scheme This is an explanation of the industry-standard Grandfather-Father-Son tape rotation schedule. This backup schedule is appropriate for most small businesses. It is a compromise of protection, convenience and performance
The total number of tapes you will require is based on your desired "restore window". A typical business with a 5-day work week will use a 20-tape rotation that will give them a one-year restore window.
Many, if not most businesses will also keep yearly tapes which can come in
handy for tax reporting purposes. For a 6-day work week ,you will need 22 tapes.
This will allow you to restore files as recent as yesterday and as old as one
year. A 6-month restore window requires 14 tapes
Number of Tapes Required
Tape LabelsDaily Tapes 4 tapes will be used every Monday through Thursday. These tapes will be used every week and will experience the most wear and tear. It is recommended the daily tapes be shifted to the monthly group once in a while so they don't wear out prematurely...like rotating the tires on your car.MondayTuesdayWednesdayThursday
Tape LabelsWeekly Tapes 4 more of your tapes will be used once a month on Fridays. (or Saturdays, depending on whether or not you are backing up a six-day workweek). Whenever it appears you need a Friday Week 5 tape, you should just use the EOM (End of Month) tape.Friday Week 1Friday Week 2Friday Week 3Friday Week 4
Tape LabelsMonthly Tapes Twelve of your tapes will be used on the last business day of each month. January EOM February EOM March EOM etc
Quantity of Tapes
Daily Tapes + Weekly Tapes + Monthly Tapes 4 + 4 + 12
Total = 20 Tapes
A 5-day work week = 20 Tapes
A 6-day work week = 22 Tapes Daily Tapes + Weekly Tapes + Monthly Tapes 5 + 5 + 12
Total = 22 Tapes
Tower of Hanoi
The Tower of Hanoi rotation schedule is widely used.
This schedule can be used in either a daily or weekly rotation scheme. The decision
regarding the frequency of rotation should be based on the volume of data traffic. To
maintain the required history of file versions, a minimum of 5 tape sets should be used in the weekly rotation schedule, or
8 for a daily rotation scheme. . As with the G.F.S rotation scheme, tapes
should be periodically removed from the rotation for archive purposes.
Tower of Hanoi
Tower of Hanoi The Tower of Hanoi rotation
method is more complex. It is based on the mathematics of the
Tower of Hanoi , using a recursive method to
optimize the back-up cycle. So the 1st tape is used every other
day (1, 3, 5, 7, 9,...),
the 2nd tape is used every 4th day (2, 6, 10, ...),
the 3rd tape is used every 8th day (4, 12, 20, ...).
Tower of HanoiA set of n tapes (or other
media) will allow backups for 2 ^n-1 days before the last set is recycled. So, 3 tapes will give 4 days' worth of backups and on
the 5th day it will be overwritten; 4 tapes will give 8 days, and it is overwritten on
the 9th day; 5 tapes will give 16 days, etc. Files can be restored from 1, 2, 4, 8, 16, ..., 2 ^n-1
days ago.
Tower of Hanoi
Tower of HanoiN= NUMBER OF TAPES
WORTH OF BACKUP IN DAYS2** (N-1)
N=3 4 DAYSN = 4 8 DAYSN = 5 16 DAYSN = 6 32 DAYS
N= NUMBER OF TAPES
WORTH OF RETENTION
IN DAYS (2**N) -1
N=3 7 DAYSN = 4 15 DAYSN = 5 31 DAYSN = 6 63 DAYS
Tower of HanoiIn this method, a set of numbered media is used until the end of the cycle. Then the cycle is repeated using media numbered the same
as the previous cycle, but incremented by one. The lowest
numbered tape from the previous cycle is retired and kept
permanently. Thus, one has access to every backup for one cycle, and one backup per cycle
before that.
Tower of Hanoi1ST CYCLE 2ND CYCLE 3RD CYCLE 4TH CYCLETAPE 1 TAPE 2 TAPE 3 TAPE 4
TAPE 2 TAPE 3 TAPE 4 TAPE 5
TAPE 1 TAPE 2 TAPE 3 TAPE 4
TAPE 3 TAPE 4 TAPE 5 TAPE 6
TAPE 1 TAPE 2 TAPE 3 TAPE 4
TAPE 2 TAPE 3 TAPE 4 TAPE 5
TAPE 1 TAPE 2 TAPE 3 TAPE 4
TAPE 3 TAPE 4 TAPE 5 TAPE 6
Observation As you can see, the lower numbered tapes get used far more frequently than higher numbered tapes. This means
that the Tower of Hanoi scheme won't retain daily backups for a
week like the other tape rotation schemes, but it does
give you exponential retention periods.
ObservationFor example, in the 5 tape rotation
scheme, Tape 1 is used 16 times (every other
day). Tape 2 is used 8 times (every 4 days). Tape 3 is used 4 times (with 7 days in
between). Tapes 4 and Tapes 5 are each used 2
times. In essence, this gives you daily and monthly backups like the other tape rotation schemes do, but you use far
fewer tapes in the long run.
Disadvantages of Tower of Hanoi The downside to this rotation
scheme is its complexity and the fact that not all backup applications support
it. This method also has a tendency to
wear out lower numbered tapes because they are used so much more frequently
than higher numbered tapes. Another disadvantage of the method is
that (short retention period)
half the backups are overwritten after only
2 days.
Round RobinRound-Robin is the simplest of tape rotations to understand. This type of cycle uses a single tape set for a set period of time, but only keeps the information for the length of that time period. However, it forces the
Administrator to frequently re-use the tapes over and over again.
Due to wear and tear, these tapes would be replace frequently. Another
con to this type of rotation is that there is no long-term storage
solution.
Round RobinExample: A weekly Round-Robin
tape rotation would mean that there are tapes marked "Monday",
"Tuesday", "Wednesday", etc. Each day’s tapes are used on that
specified day of the week, and then re-used 7 days later
Round RobinOne other simple scheme is to have 5 backup tapes (one for each day of the
work week) and to use each one in succession. This way, you use the same tape every day of the week. For extra
protection, you can use more than one tape for one day of the week, say Friday, and rotate the Friday tape offsite every week. This system pretty much requires that you do a full backup every day. This may be fine for a small business
without a lot of data to preserve, but it can mean a good-sized backup window
every day.
Limitations of Round Robin The biggest problem with the Round Robin variations is that it doesn’t support long-
term data retention, which is very important to have in a data backup plan.
To see why this is important, imagine that an organization uses a 4-week tape
rotation scheme. Now suppose that an organization finds that a critical file has been corrupted. If the corruption occurred more than four
weeks ago, then there are no good copies of
the file that can be retrieved from backup. For this reason, most of the organizations
that use Round Robin also use data archiving.
Recommendations: Small organizations There are many small organizations who can fit all of their data files onto a single tape. Since backing up this small amount
of data does not take much time, many small organizations prefer to do full
backups on a daily basis, and to rotate their tapes in a round-robin strategy.
Assuming there are no actual IT personnel staffed by the company, this
method of daily full backups puts everyone’s mind at ease and does not
require a large collection of tapes. However, keep a couple of spare tapes on-
hand in the event one of them breaks.
Recommendations: Medium organizationsCompanies of this size usually prefer to
implement a G.F.S rotation method. Since this size of organization probably has a
small IT staff, they should all be made aware of how the backup jobs and tape rotations
are implemented. To prevent confusion, the dates of the backups and their associated
tapes should be documented for future reference. The actual backup methods
depends on your needs, but a minimum of the following is recommend… Monthly Full backups, Weekly Incremental backups, and
Daily Differential backups.
Recommendations: Large organizations It is assumed that large organizations will
have a large IT staff. Backup Administrators will be responsible for
managing to a large amount of data which will no doubt be changing very fast. To that end, they will most likely prefer to tighten up the backup jobs to require Differential backups to be performed every couple of
hours, Incremental backups every evening, and Full backups a minimum of once per week. The tape rotation would also be at the Backup Administrators discretion.
Note that any backup system absolutely depends on daily attention and periodic
maintenance. Every backup system requires a
"backup administrator" to change the tapes every day, to store them in the
proper location and to monitor the backup logs for any errors.
Periodically, every backup system needs to be tested in order to be sure data
is actually being backed up and can be restored when needed. Tape drives also need to be periodically cleaned. With most tape drives, this generally means occasionally inserting a cleaning tape.
Reliability
In the end, there is no one single backup tape rotation scheme that
is clearly superior. Each tape data backup scheme has
inherent advantages and disadvantages. It is ultimately up
to you to choose the scheme that is the best fit for your organization's
needs.
Conclusion
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