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Lies, damned lies, and statistics!
If you have read my three previous posts (1, 2, 3), you may walk away with an impression that on a drive presented from a high-end enterprise class disk array, Windows file fragmentation does not have a significant performance impact. And I’ve given you empirical data—oh yeah, statistics—to support that ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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