sata raid

[vbsaltydog]

Hey gang, I am trying to beef up a client's (WIMP) Windows, IIS, MySQL, PHP Web Server. It is an emachine 2542 that does not have sata controllers built in to the mobo.
His server runs great but now that he is hosting perl based shopping carts he needs faster seek times. He has a gig of RAM so memory is OK and a large swap file so this is not his speed issue nor is his processor as CPU stats are within norms.
I recommended a 10K hard drive such as the Western Digital Raptor series and perhaps disk striping for speed and failover in a raid 5 setup. So my question is now...any ideas on a good method for adding sata raid (hardware raid preferred) in a raid 5 setup using raptor drives in a emachine 2542.
I know, i know..why the emachine? The short answer is that he has alot of time in the server and doesnt want to migrate at this time to a server class box.

Any advise?

Thanks to all.

 

[xmsre]

I take it in't not space we're worried about, but performance. Let's look at some numbers.

For a SCSI 10K RPM drive, assuming 20ms IO, a single spindle can support 85 IOPS.

For a SCSI 15K RPM drive, the number is 110 IOPS

For SATA 7200 RPM drives, it's 36 IOPS

For SATA 10K RPM drives, it's 48 IOPS.


Now, when we combine spindles into RAID sets, we need to calculate the performance of the RAID set. Read and Write performance dirrer with several types of RAID, so we'll calculate read and write performance seperately.

For RAID 1 or 0+1, or 10,

Read performance = P * N where P is the performace of a spindle and N is the number of spindles that comprise the RAID set.

Write performance = P * N/2

For RAID 5,

Read performance = P * (N-1)

Write performance = P * (N-1)/4


Now, let's look at some scenarios with 4 spindles

4 SATA 10K RPM Drives RAID 10

Read performance = 48 *4 = 192 IOPS
Write Performance = 48 * 4/2 = 96 IOPS

4 SATA 10K RPM Drives RAID 5

read performance = 48 * (4-1) = 144 IOPS
write Performance = 48 *(4-1)/4 = 36 IOPS

4 SCSI 10K RPM Drives RAID 10

Read Performance = 85 * 4 = 340 IOPS
Write performance = 85 *4/2 = 170 IOPS

4 SCSI 10K RPM Drives RAID 5

Read Performance = 85 * (4-1) = 255 IOPS
Write Performance = 85 * (4-1)/4 = 63.75 IOPS

From this little exercise we can conclude that if performance counts, don't use SATA or RAID 5. SATA and RAID 5 are suited for applications where space, not performance, is the determining factor. When performance is critical, use SCSI and RAID 1/0+1/10.

 

[vbsaltydog]

Thank you for a very well explained answer. Per your info I have suggested that the client go with a scsi array and a server level hardware solution.

Thanks again for helping out with this!

-vbsaltydog

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