Upgrading to SAS drives

We were having some disk drive performance issues at a client recently.  They have a 6 drive array running RAID 10.  We spent some time running SQLIO against the array.  Our standard test was an 8KB random read with a queue depth of eight.  The array was giving us 370 I/O operations per second with a latency of 42 ms.  We cracked open the case and discovered it was using 7200 RPM SATA drives.  We replaced the controller with the same model except that it was designed for SAS (serially attached SCSI) and installed six 15,000 RPM SAS drives.  Running the identical test now resulted in 1,980 I/O operations per second with a 7 ms latency.  Nice! 

Next, we rebuilt the partition using DISKPART.EXE to align the partitions.  (Yes, I know the instructions are for Exchange.  But that's the best description I've found and that's exactly what we did.)  We used a setting of 64 for the alignment.  That improved our performance to 2,142 and 6 ms latency.  Aligning the partitions increased our I/O throughput by just over 8%.

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