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Showing page 2 of 2 (19 total posts)
  • Performance Impact: file fragmentation and SAN – Part III

    256KB Sequential Reads   In my two previous posts (1, 2), I highlighted the fact that while file fragmentation had a huge adverse performance impact on directly attached storage (DAS), it did not have much, if any, impact on the drive presented from a high end enterprise class disk array. That observation was derived from running disk I/O ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on December 10, 2008
  • 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 ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on December 8, 2008
  • Performance Impact: file fragmentation and SAN -- Part I

    1KB Sequential Writes   It’s well known that disk I/O performance can be severely impacted by fragmentation at the file system level. In other words, when a file is allocated space from many small fragments, its performance can be much worse than when its space is allocated from a single contiguous chunk. The impact is most pronounced with ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on December 7, 2008
  • SQL Server and SANs: The QueueDepth Setting of a Host Bus Adapter (HBA)

    Too many DBAs tend to view a drive presented from a Storage Area Network (SAN) as something of a monolithic nature. They look at the drive as if it had some intrinsic performance characteristics. This view doesn't help one appreciate the true performance characteristics of such a drive. A more constructive view is to look at the drive as an I/O ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on September 18, 2007
  • How to Corrupt a SQL Server 2005 Database

    How can you corrupt an online SQL Server 2005 database? Okay, why would you want to do that? Well, let's say because you want to test out some DBCC commands. If you take a SQL Server 2005 database offline, you can easily corrupt it by opening it with a different program and messing up the file content. But then it's unlikely you can ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on August 29, 2007
  • How did Random I/Os Outperform Sequential I/Os?

    Recently, when I was doing some I/O performance tests on an I/O path, I found that 8K random reads (and writes) significantly and consistently outperformed 8K sequential reads (and writes) in terms of I/O throughput (megabytes per second). I was puzzled. With a traditional hard disk that is made up of a stack of magnetic platters held by a ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on April 4, 2007
  • Should I Use a Windows Striped Volume?

    In Windows Server 2003, you can use the Disk Management console to create a striped volume over multiple dynamic disks (well, you can also create a mirrored, a RAID-5 volume, etc). If these disks (or LUNs) are presented from a SAN, most likely you can stripe across the same storage devices--making up these LUNs--inside the SAN to present ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on March 12, 2007
  • Is RAID 5 Really That Bad?

    RAID 5 is a dirty word in the DBA community and beyond. There are websites devoted to trash RAID 5. I've seen DBAs declaring performance root cause found the very moment they found out that some database files were placed on RAID 5 volumes. You'd be ridiculed and run out of town if you dare to suggest putting the transaction log file on RAID ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on February 7, 2007
  • Beware of Shifting SAN

    Let’s say you are trying to determine the performance impact of a neat database design change you have just devised on an application. So you run some tests with the existing design and the tests run for several hours. Coming back the next day, you make the change and re-run the same tests. The test results look fantastic. Now, before you ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on January 3, 2007
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