Disk IO measuring

Last Post 03 Jun 2009 08:49 PM by TRACEYSQL. 0 Replies.
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03 Jun 2009 08:49 PM
HI i like to bench mark current IO on sql and determine if the SAN is set up correctly for volume of transactions.

I have found the following thread.

Physical Disk\Avg. Disk Reads/Sec and Physical Disk\Avg. Disk Writes/Sec

When using above counters, you may need to adjust the values for RAID configurations using the following formulas.

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

For example, you have a RAID-1 system with two physical disks with the following values of the counters.

Disk Reads/sec 80

Disk Writes/sec 70

Avg. Disk Queue Length 5

In that case, you are encountering (80 + (2 * 70))/2 = 110 I/Os per disk and your disk queue length = 5/2 = 2.5 which indicates a border line I/O bottleneck.

(........borde line 2.5 what is the border line to what out for)..?

Disk I/O issues can be minimized by having larger and sequential I/O activities. To achieve than you should consider partitioning. Partitioning can be done in many ways – Database partitioning, Tempdb partitioning, Table partitioning, index partitioning. At a minimum, it is highly recommended to partition your database in such a way that clustered index, non-clustered index, and transaction logs are each on a separate physical drive and spread across multiple logical filegroups/files within that drive.

So i got the following from one of the DISK S from permon and did all disks separately to log results

Avg Disk Sec Write * the results by 1000 to get ms
0.003127594 3.127594
0.345726198 345.726198 (rather high to me)..........
0.000120349 0.120349
0.0001653 0.1653

Now do i need to determine that S on the SAN (has x number of disks).
Raid 10 -- I/Os per disk = [reads + (2 * writes)] / number of disks
(How do i determine the number of disks to divide by ? on permon i select each disk).
Is this number of disks something i need to ask SAN Guys how many disks in (DISK S)?

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