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: 2014-07-24  |  Article URL http://www.symantec.com/docs/TECH64105
Article Type
Technical Solution

Product(s)

Issue



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

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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:
  • Adaptec Ultra 320 SCSI
     

Supplemental Materials

SourceUMI
ValueV-259-0013
Description

If you choose a block size that is larger than 64KB, you may not be able to restore the data



Legacy ID



311736


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


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