46130: Acronis Backup Advanced 11.5: Tape Write Block Size Cannot Be Changed

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Operating Systems: 

Last update: 13-07-2017

Does not apply to Acronis Backup Advanced 11.7, see this topic.


You may observe following behavior:

  • Backup to a tape device shows low performance.
  • Write speed to the tape device with other software is noticeably higher.
  • Backup to local HDD or to other media is noticeably faster.
  • Tape drive shows "stop & go" behavior, constatly changing from writing to idle state.


Acronis Backup Advanced 11.5 detects the block size as 16 KB and uses it for all write operations. At the same time your tape device is optimized to work with large block sizes (32 KB and higher).

Devices optimized to work with larger block sizes show "stop & go" behavior, since the tape drive fails to contineously write the smaller blocks to the tape media. This may noticeably reduce the total backup performance.


There is no possibility to change the setting for the write block size on the tape device. This feature will be added to the next versions of the product.

To get more information about the issue, contact Acronis Customer Central.

More information

To make sure that the issue with slow write speed to tape is caused by the block size, do the following:

  • Go to the article Tape Detection Tools.
  • Download the sptd.exe tool.
  • Use the tool and perform writing with different block sizes: 16384, 32768, 65536, 131072 etc. until you reach the best/expected performance.
  • If you see that write speed with small block size is as small as the backup speed, and the write speed with large block size shows better performance, it confirms the above described behavior.