SQL Server Performance Forum – Threads Archive

Formulas to Calculate RAID Performance?

What formula exist to calculate RAID performance? I would like to compare RAID 0+1, 5 and 10. I know the forumla deals with I/O per second, but I don’t recall its syntax. Thanks, Dave

I can’t help with formula, but the following may be help: http://www.sql-server-performance.com/ew_san.asp
http://www.sql-server-performance.com/q&a38.asp
Luis Martin …Thus mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true.
Bertrand Russell

The book MicrosoftÂ® SQL Server 2000â„¢ Performance Tuning Technical Reference @http://www.microsoft.com/mspress/books/4944.asp has excellent discussion on this topic. Gaurav
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Good site for raid information: http://www.acnc.com/04_01_00.html -Muhammed

RAID 0: I/Os per Disk = (Reads + Writes) / Number of Disks RAID 1: I/Os per Disk = [Reads + (2*Writes)]/2 RAID 5: I/Os per Disk = [Reads + (4*Writes)] / Number of Disks RAID 10: I/Os per Disk = [Reads + (2 * Writes)] / Number of Disks

That’s exactly what I was looking for. How did you find this information? Thanks, Dave

in raid 1 or 10, 1 logical write requires 2 physical disk writes
in raid 5, 1 logical write require 1 physical read of the data block, 1 read for the parity, 1 write for the data, 1 write for the parity for a total of 4 I/Os

Thanks for the help. Dave

Hi ykchakri and all! I’m joining this thread late, since I’m new to the forum and just read about it…
In the RAID 10 formula, by "number of disks" do you mean physical or logical disks? That is, if I have a 4 disks RAID 10 array, do I have to count 4 (for the physical disks), or just 2 (for the 2 mirrors that build the RAID 10 volume)? Thanks.

quote:Originally posted by ykchakri RAID 0: I/Os per Disk = (Reads + Writes) / Number of Disks RAID 1: I/Os per Disk = [Reads + (2*Writes)]/2 RAID 5: I/Os per Disk = [Reads + (4*Writes)] / Number of Disks RAID 10: I/Os per Disk = [Reads + (2 * Writes)] / Number of Disks

the formulas apply to actual physical disks, not the physical disks in Windows Disk Management. Suppose you have a HW RAID controller, Use the Windows physical disk counters (MS seems to suggest the logical counters are expensive to maintain) the performance counters the Operating System reports is for the logical drive presented by the RAID controller.
So, if the OS reports 100 reads and 100 writes from a RAID 10 logical drive, the IO going to the actual physical drives is: 100 for the reads, and 200 for the 100 writes (100 for each part of the mirrored set)

Also remember that the stripe size for RAID is significantly smaller for RAID 5 then other forms of RAID, making the read/write performance even worse Cheers
Twan

and what about RAID15? how is the perfomance calculated?

Mitya, welcome to the forums.
Please start a new thread. This one is 9 years old.

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