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Linchi Shea

Checking out SQL Server via empirical data points

Performance impact: file fragmentation and SAN – Part II

1KB Sequential Writes on DAS


There were some questions about the use 1KB sequential writes in my previous post to test the performance impact of file fragmentation on a drive presented from a high end enterprise class disk array.


There were two reasons for testing 1KB sequential writes:

·      SQL Server may write to a transaction log in 1KB sequential writes.

·      File fragmentation can have a devastating impact on 1KB sequential writes on a directly attached drive.


To highlight the contrast, I’m posting the results that I did a quite while ago on a RAID-1 set that consisted of two internal disks. The test setup was exactly the same as described in Performance impact: file fragmentation and SAN – Part I. The only difference was the target disks were now directly attached. The results are summarized as follows:

As the chart shows, the file fragmentation had caused the throughput to drop 33% from ~60MB/sec to ~40MB/sec on this directly attached RAID-1 set.


Nothing is new here. It is worth posting for comparison purposes only.


Published Monday, December 08, 2008 2:49 PM by Linchi Shea

Attachment(s): 1KDAS.gif



Brent Ozar said:

I'm excited to see you blogging again, sir!  I missed your disk metrics.  Keep up the good work - this is one of the things that takes DBAs forever to do, and it's hard to work it into a DBA schedule.  Good stuff.

December 8, 2008 2:29 PM

James Luetkehoelter said:

Ooo, nice Linchi. I run into many a SAN administrator who is adamant that fragmentation just "doesn't happeon on a SAN, and if would the impact would be negligible".

Great to have quantitative validation!

December 8, 2008 7:12 PM

Linchi Shea said:

256KB Sequential Reads In my two previous posts ( 1 , 2 ), I highlighted the fact that while file fragmentation

December 10, 2008 12:19 PM

Linchi Shea said:

Lies, damned lies, and statistics! If you have read my three previous posts ( 1 , 2 , 3 ), you may walk

December 22, 2008 11:40 AM
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