HP StoreOnce 4430 HP StoreOnce Backup System Concepts and Configuration Guidel - Page 66

Cartridge sizing, Number of libraries per appliance, Backup application and configuration

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(which may include the library device). The same limitation could be hit with multiple libraries and fewer drives per library. • A similar limitation exists for Fibre Channel. Although there is a theoretical limit of 255 devices per FC port on a host or switch, the actual limit appears to be 128 for many switches and HBAs. You should either balance drives across FC ports or configure less than 128 drives per library. • Some backup applications will deliver less than optimum performance if managing many concurrent backup tape drives/streams. Balancing the load across multiple backup application media servers can help here. Cartridge sizing The size of a virtual cartridge has no impact on its performance and cartridges do not pre-allocate storage. It is recommended that cartridges are created to match the amount of data being backed up. For example, if a full backup is 500 GB, the next larger configurable cartridge size is 800 GB, so this should be selected. Note that if backups are to be offloaded to physical media elsewhere in the network, it is recommended that the cartridge sizing matches that of the physical media to be used. Number of libraries per appliance The StoreOnce appliance supports the creation of multiple virtual library devices. If large amounts of data are being backed up from multiple hosts or for multiple disk LUNs on a single host, it is good practice to separate these across several libraries (and consequently into multiple backup jobs). Each library has a separate deduplication "store" associated with it. Reducing the amount of data in, and complexity of, each store will improve its performance. Creating a number of smaller deduplication "stores" rather than one large store which receives data from multiple backup hosts could have an impact on the overall effectiveness of deduplication. However, generally, the cross-server deduplication effect is quite low unless a lot of common data is being stored. If a lot of common data is present on two servers, it is recommended that these are backed up to the same virtual library. • For best backup performance, configure multiple virtual libraries and use them all concurrently. • For best deduplication performance, use a single virtual library and fully utilize all the drives in that one library. Backup application and configuration In general backup application configurations for physical tape devices can be readily ported over to target a deduplicating virtual library with no changes; this is one of the key benefits of virtual libraries - seamless integration. However considering deduplication in the design of a backup application configuration can improve performance, deduplication ratio or ease of data recovery so some time spent optimizing backup application configuration is valuable. Blocksize and transfer size As with physical tape, larger tape block sizes and host transfer sizes are of benefit. This is because they reduce the amount of overhead of headers added by the backup application and also by the transport interface. The recommended minimum is 256 KB block size, and up to 1 MB is suggested if the backup application and operating system will support this. For HP Data Protector and EMC Networker Software a block size of 512 KB has been found to provide the best deduplication ratio and performance balance and is the recommended block size for this application. Some minor setting changes to upstream infrastructure might be required to allow backups with greater than 256 KB block size to be performed. For example, Microsoft's iSCSI initiator 66 Virtual Tape Devices

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(which may include the library device). The same limitation could be hit with multiple libraries
and fewer drives per library.
•
A similar limitation exists for Fibre Channel. Although there is a theoretical limit of 255 devices
per FC port on a host or switch, the actual limit appears to be 128 for many switches and
HBAs. You should either balance drives across FC ports or configure less than 128 drives per
library.
•
Some backup applications will deliver less than optimum performance if managing many
concurrent backup tape drives/streams. Balancing the load across multiple backup application
media servers can help here.
Cartridge sizing
The size of a virtual cartridge has no impact on its performance and cartridges do not pre-allocate
storage. It is recommended that cartridges are created to match the amount of data being backed
up. For example, if a full backup is 500 GB, the next larger configurable cartridge size is 800
GB, so this should be selected.
Note that if backups are to be offloaded to physical media elsewhere in the network, it is
recommended that the cartridge sizing matches that of the physical media to be used.
Number of libraries per appliance
The StoreOnce appliance supports the creation of multiple virtual library devices. If large amounts
of data are being backed up from multiple hosts or for multiple disk LUNs on a single host, it is
good practice to separate these across several libraries (and consequently into multiple backup
jobs). Each library has a separate deduplication “store” associated with it. Reducing the amount
of data in, and complexity of, each store will improve its performance.
Creating a number of smaller deduplication “stores” rather than one large store which receives
data from multiple backup hosts could have an impact on the overall effectiveness of deduplication.
However, generally, the cross-server deduplication effect is quite low unless a lot of common data
is being stored. If a lot of common data is present on two servers, it is recommended that these
are backed up to the same virtual library.
•
For best backup performance, configure multiple virtual libraries and use them all concurrently.
•
For best deduplication performance, use a single virtual library and fully utilize all the drives
in that one library.
Backup application and configuration
In general backup application configurations for physical tape devices can be readily ported over
to target a deduplicating virtual library with no changes; this is one of the key benefits of virtual
libraries – seamless integration. However considering deduplication in the design of a backup
application configuration can improve performance, deduplication ratio or ease of data recovery
so some time spent optimizing backup application configuration is valuable.
Blocksize and transfer size
As with physical tape, larger tape block sizes and host transfer sizes are of benefit. This is because
they reduce the amount of overhead of headers added by the backup application and also by the
transport interface. The recommended minimum is 256 KB block size, and up to 1 MB is suggested
if the backup application and operating system will support this.
For HP Data Protector and EMC Networker Software a block size of 512 KB has been found to
provide the best deduplication ratio and performance balance and is the recommended block size
for this application.
Some minor setting changes to upstream infrastructure might be required to allow backups with
greater than 256 KB block size to be performed. For example, Microsoft’s iSCSI initiator
66
Virtual Tape Devices