HP 12000 HP VLS Solutions Guide Design Guidelines for Virtual Library Systems - Page 30

Blocksize and Transfer Size, LAN-free Backups, Retention Planning, If you are not using deduplication

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but the remaining half of the drives in the library can still be used and can still access every virtual cartridge in the library. This also implies that when a SAN fabric fails this halves the available Fibre Channel performance so if full backup performance is required even after a SAN fabric failure then the VLS needs to be configured with double the number of Fibre Channel ports. Instead of configuring dual path virtual tape drives, it is better to configure single-path virtual tapes across multiple Fibre Channel ports that are connected to both SAN fabrics. Also , if the VLS has multiple nodes, ensure that each media server has multiple paths to each VLS node so that if a secondary node fails the media server can continue operations on the remaining nodes. Blocksize and Transfer Size As with physical tape, larger tape block sizes and host transfer sizes are of benefit; they reduce the amount of overhead of headers added by the backup application and the transport interface. HP recommends a blocksize of 256 KB (the maximum supported) for the VLS. LAN-free Backups All enterprise backup applications provide the ability to run "LAN-free" backups. This is where application servers connected to the SAN run the backup media agent and can perform backups directly over the SAN to the tape library. This removes this backup traffic from the LAN and speeds up backups (by removing the LAN performance bottleneck). One of the disadvantages of LAN-free backup to a physical library is that it cannot be multiplexed because each backup stream is written directly from the data source to the tape drive, and so it could generally only be used with the largest application servers which can supply high speed backup streams. One of the key advantages of a SAN virtual library is the ability to increase the amount of LAN-free backup used. With a virtual library you do not have to provide maximum performance per LAN-free backup stream as needed on physical tape drives. You can create many virtual drives and thus enable LAN-free backup on any SAN-connected appliance servers (regardless of their performance) that are large enough to bother with LAN-free backup. This improves the backup performance of the LAN-free backups and also improves performance of the remaining LAN backups because the LAN-free backup traffic has been removed from the LAN. Retention Planning Retention planning and sizing go hand in hand. How long do you need to keep data on disk? How many full backups do you want to keep on disk? How many incremental backups? How do you want to optimize retention times of the VLS? Retention policies help you recycle virtual media. Bear the following considerations in mind as you plan retention policies: • If you are not using deduplication, you can retain the data on the disk backup device for a shorter period such as 1-2 weeks (because more than 90% of restores generally occur within the first week's retention of backups) and then use tape copies to retain data for longer periods. • If you are using deduplication, you can retain data on your disk backup device with the same level of retention times as you would have had on tape. This provides a more granular set of recovery points with a greater likelihood that a file that you need to recover will be available for longer and in many more versions. To use deduplication-enabled replication you must have at least two full backups retained on the disk backup device. • Once the retention period expires, the virtual media is automatically recycled. • You should set the tape expiration dates (that is, when the tape is marked as worn out) high because virtual media does not wear out. • Backup-job retention time is for virtual media. • Copy-job retention time is for physical media. • When copying through the backup application, the virtual and physical pieces of media are tracked separately and the retention times should be considered and set individually. 30 Backup Solution Design Considerations

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but the remaining half of the drives in the library can still be used and can still access every virtual
cartridge in the library. This also implies that when a SAN fabric fails this halves the available
Fibre Channel performance so if full backup performance is required even after a SAN fabric
failure then the VLS needs to be configured with double the number of Fibre Channel ports. Instead
of configuring dual path virtual tape drives, it is better to configure single-path virtual tapes across
multiple Fibre Channel ports that are connected to both SAN fabrics. Also , if the VLS has multiple
nodes, ensure that each media server has multiple paths to each VLS node so that if a secondary
node fails the media server can continue operations on the remaining nodes.
Blocksize and Transfer Size
As with physical tape, larger tape block sizes and host transfer sizes are of benefit; they reduce
the amount of overhead of headers added by the backup application and the transport interface.
HP recommends a blocksize of 256 KB (the maximum supported) for the VLS.
LAN-free Backups
All enterprise backup applications provide the ability to run “LAN-free” backups. This is where
application servers connected to the SAN run the backup media agent and can perform backups
directly over the SAN to the tape library. This removes this backup traffic from the LAN and speeds
up backups (by removing the LAN performance bottleneck). One of the disadvantages of LAN-free
backup to a physical library is that it cannot be multiplexed because each backup stream is written
directly from the data source to the tape drive, and so it could generally only be used with the
largest application servers which can supply high speed backup streams.
One of the key advantages of a SAN virtual library is the ability to increase the amount of LAN-free
backup used. With a virtual library you do not have to provide maximum performance per LAN-free
backup stream as needed on physical tape drives. You can create many virtual drives and thus
enable LAN-free backup on any SAN-connected appliance servers (regardless of their performance)
that are large enough to bother with LAN-free backup. This improves the backup performance of
the LAN-free backups and also improves performance of the remaining LAN backups because the
LAN-free backup traffic has been removed from the LAN.
Retention Planning
Retention planning and sizing go hand in hand. How long do you need to keep data on disk?
How many full backups do you want to keep on disk? How many incremental backups? How do
you want to optimize retention times of the VLS? Retention policies help you recycle virtual media.
Bear the following considerations in mind as you plan retention policies:
•
If you are not using deduplication, you can retain the data on the disk backup device for a
shorter period such as 1-2 weeks (because more than 90% of restores generally occur within
the first week’s retention of backups) and then use tape copies to retain data for longer periods.
•
If you are using deduplication, you can retain data on your disk backup device with the same
level of retention times as you would have had on tape. This provides a more granular set of
recovery points with a greater likelihood that a file that you need to recover will be available
for longer and in many more versions. To use deduplication-enabled replication you must
have at least two full backups retained on the disk backup device.
•
Once the retention period expires, the virtual media is automatically recycled.
•
You should set the tape expiration dates (that is, when the tape is marked as worn out) high
because virtual media does not wear out.
•
Backup-job retention time is for virtual media.
•
Copy-job retention time is for physical media.
•
When copying through the backup application, the virtual and physical pieces of media are
tracked separately and the retention times should be considered and set individually.
30
Backup Solution Design Considerations