Selecting block size greater than 64KB in the tape device properties,brings up the following warning message-"If you choose a block size that is larger than 64KB, you may not be able to restore the data."

Article:TECH64105

Created: 2008-01-16

Updated: 2012-06-27

Article URL http://www.symantec.com/docs/TECH64105

Article Type
Technical Solution

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Problem

Selecting block size greater than 64KB in the tape device properties brings up the following warning message-"If you choose a block size that is larger than 64KB, you may not be able to restore the data."

Error

If you choose a block size that is larger than 64KB, you may not be able to restore the data. Before you put a changed block size setting into general use, you should thoroughly test the changes. Ensure also that backups are verified.

See the following technote before you change a block size setting : V-259-0013

Solution

All LTO and most other new models of tape drives support greater than a 64KB block size when attached to most Host Bus Adapters (HBAs). This larger block size may or may not have a performance benefit to operations. There is a risk with increasing the block size past 64K when there are multiple environments, such as different hardware for at a recovery site, using IDR with dissimilar hardware, or in a shared storage environment. Generally HBAs (and their drivers) may place different limitations on the range of useable block sizes. If a tape is written with a block size greater than 64KB, then all environments must be able to handle the chosen block size. For example, on a SAN (Storage Area Network), ensure that all servers can use the desired block size by performing test backups and restores of data.

General recommendations for working with a configuration with big block sizes:

Update all HBA drivers and firmware, use the same version and type of drivers (i.e. SCSIPort or STORPort) where possible.
In a shared storage environment, all the servers should be set to use the same block size.
In a shared storage environment with mixed HBA vendors/models, please note that not all HBAs have the same restrictions. For example, HBA vendor 1 allows 512 KB block size and HBA vendor 2 allows 256 KB. The disaster recovery site is capable of using 256 KB block size. The shared storage should be configured to use at most 256 KB block size.
Test restores at the recovery site after increasing the block size or when hardware changes at either site.

HBAs known to not support big block transfers: