SIZE_DATA_BUFFERS in Windows 2008

[hkyeakley]

I know, I know.... not another tuning thread.

Environment:

Master: RHEL 5 running NBU 7.1

Media #1: RHEL 5 running NBU 7.1

Media #2: RHEL 5 running NBU 7.1

I'm setting up a windows media server to function as my VMWare backup host. I've setup the media server, configured it to talk to my vcenter server and I can successfully test backups.

I go to tune it and I check my media. I'm using LTO 4, which, unless I'm completely misreading the user manual from IBM, has a maximum block size of 16 MB. My Qlogic HBA only supports up to 4 MB/block, and according to Google searches on how to configure the Scatter/Gather registry key, the maximum value is 255 (decimal) which grants a 1 MB block size for transfers.

I've set my MaximumSGList key and set SIZE_DATA_BUFFERS to 1048576. When I go to test a backup, I get the following:

 11/08/2011 07:55:11 - Error bptm (pid=8948) The tape device at index -1 has a maximum block size of 524288 bytes, a buffer size of 1048576 cannot be used
11/08/2011 07:55:11 - Warning bptm (pid=8948) media id N03330 load operation reported an error
11/08/2011 07:55:11 - current media N03330 complete, requesting next media Any
11/08/2011 07:56:06 - Info bptm (pid=8948) Waiting for mount of media id N03330 (copy 1) on server server-name.
11/08/2011 07:56:04 - Waiting for scan drive stop IBM.ULTRIUM-TD4.017, Media server: server-name
11/08/2011 07:56:06 - granted resource  N03330
11/08/2011 07:56:06 - granted resource  IBM.ULTRIUM-TD4.017
11/08/2011 07:56:06 - granted resource  arc-mcac-b010-hcart-robot-tld-0
11/08/2011 07:56:06 - mounting N03330
11/08/2011 07:56:48 - Error bptm (pid=8948) The tape device at index -1 has a maximum block size of 524288 bytes, a buffer size of 1048576 cannot be used
11/08/2011 07:56:48 - Warning bptm (pid=8948) media id N03330 load operation reported an error
11/08/2011 07:56:48 - current media N03330 complete, requesting next media Any 

If I set the SIZE_DATA_BUFFERS to 512k, my backups run. And quite frankly, they run fine. The 512k block size gives me acceptable throughput. I'd just like to know why the 1MB block size isn't working given the configuration for the rest of my environment.

Thank you.

[Marianne]

This has always worked for me:

To determine max SIZE_DATA_BUFFERS, load a tape into a drive (using robtest), then use the method described in TechNote :  http://www.symantec.com/docs/TECH22746   (ignore the title of the TechNote).

Look for "maximum blocksize"in the output.

[Omar_Villa]

You can only use blocks bigger than 256KB when you are going straight to disk and the media server owns the disk in this case the error message is very clear:

11/08/2011 07:55:11 - Error bptm (pid=8948) The tape device at index -1 has a maximum block size of 524288 bytes, a buffer size of 1048576 cannot be used
 

reduce your block size to 256 and you'll be fine.

[Will_Restore]

Jus make sure your restores run as well!

[Marianne]

Opening post marked with "I need a solution".... but no response to suggestions?...  

[Douglas_A]

IBM LTO4 drives have a max block size of 256k, this is usually the optimaly setting for your buffer size. However if you are staging to disk then off to tape use the SIZE_DATA_BUFFERS_DISK and SIZE_DATA_BUFFERS options together having set the DISK buffer to 1MB.

[Charles_Buqakey]

block sizes for LTO 4 can be in excess of 1MB, however operating system or driver configurations may place a soft limit on what value an application can utilize. the effectiveness of these larger block sizes would obviously be based on how well data is streamed to the drive.

cheers

[Marianne]

It seems that

hkyeakley is no longer following this thread or forum... NO response since original post 2 months ago....