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."
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
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:
- Adaptec Ultra 320 SCSI