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Generally poor tape backup performance on a new Windows 2008 Enterprise server

Posted on 2009-05-01
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I purchased a new Dell PowerVault 124T (LTO-2) and installed it on a new quad Xeon PowerEdge.  It's the only device on the Adaptec 39160 bus, but I've eliminated the SCSI bus since I'm getting nominal verify performance (1-3GB/min).  I'm using BE 12.5 with SP1 and a hotfix that Dell had me install.  I've installed the latest firmware on the drive and autoloader.  The server has two local partitions (C:, E:) that are physical SATA II drives.  I'm running ESET Nod32 3 and I believe Windows Indexing is turned on for these two drives.  The drives have 0 fragmentation according to Diskeeper 2009.

I've run several tests serveral times, and here's what I've come up with on average:

1. Selecting the entire server to backup (system state, etc.) produces the slowest result.  About 650MB/min.  This is about 50% of the worst case spec (1.44GB/min native, no compression).

2. Selecting E drive (about 24GB) is slightly better, at 735MB/min.

3. Selecting C:\Temp where I created 80 300MB highly compressible files produced varying results.  Four tests fluctuated from 1.44GB/min to 4.5GB/min.

This server isn't in production yet, so there were no activities demanding CPU (other than the backup) when these tests were run.  Also, backup takes about 1-2% of CPU.  The server has 4GB RAM, and I'm not getting excessive paging.  For BE I'm using hardware compression, and the default block size is 64KB, buffer 64KB, buffer count=10, high water count=0.  Write single block mode and Write SCSI pass-through mode are both checked (all of these values are BE's defaults for this device, which I have unchanged).

Thanks for hanging there so far.  My question of course is why am I getting half the worst-case spec in a traditional backup scenario?  I expect that even where I'm backing up tons of small files that aren't compressible, I should be getting 1.44GB/min as an absolute minimum.  It appears as if the drive is capable, but BE or something affecting the write capability of the drive isn't configured properly?

Thanks for the help, in advance.
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Question by:z0ner
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Author Comment

by:z0ner
ID: 24282563
I was thinking that maybe NOD32 AV or Windows Indexing is slowing down the write performance - is this possible?  

The read seems fast which only NOD could affect, and Windows Indexing would slow down a write, but only to disk and not tape, correct?
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by:TapeDude
ID: 24283289
"Write single block mode" is your problem.

Use a larger buffer, too - some multiple of 64k, like 640k or 6400k.

You want to be writing multiple blocks in fixed block mode as this cuts down I/O overhead to a minimum.

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Author Comment

by:z0ner
ID: 24283460
Thanks TapeDude, I'll try that immediately and let you know.  It makes perfect sense.

In BE however, the only choices I have for buffer size are 32KB, 64KB, 128KB, 256KB, 512KB, and 1MB.  Should I just try 512KB and 1MB?  Also, after making these changes should I be powercycling the tape drive, Windows 2008, or stopping/starting BE services?
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TapeDude earned 2000 total points
ID: 24283566
1MB buffer should do the trick - that's 16 x 64k blocks. If the system has problems with this, try reducing the number of buffers before reducing the buffer size.

You shouldn't need to powercycle the drive or Windows, but it might be an idea to stop/start the BE tape engine. It all depends on whether the software authors decided to check the device settings every time a new backup is started, or just when the tape engine starts up.

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Author Comment

by:z0ner
ID: 24286957
I went ahead and implemented a buffer of 1024KB, and a buffer count of 32.  I also unchecked the write single block mode.  Although it increased my "everything" backup from 650 to 800MB/min, I still wish I'd get the advertised rates.

My 20GB highly compressible data went through the roof, at almost 6GB/min.  And my restore operation is solid at 1.5GB/min.

Thanks for your suggestions, and steering me in the right direction.
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