HW Raid poor io performance Post: 302461302

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Top Forums UNIX for Advanced & Expert Users HW Raid poor io performance Post 302461302 by roli8200 on Sunday 10th of October 2010 03:53:43 AM

10-10-2010

Registered User

HW Raid poor io performance

Hello all

We just built a storage cluster for our new xenserver farm. Using 3ware 9650SE raid controllers with 8 x 1TB WD sata disks in a raid 5, 256KB stripe size.

While making first performance test on the local storage server using dd (which simulates the read/write access to the disk mostly equal as the iscsi target does it later) we see very strange performance values.

Using the default dd (with the hardware reported block size of 512bytes) directly on the device (/dev/sdb) gives around 44MB/s write performance.

Using dd with a 1MB blocksize (bs=1M) gives around 587MB/s write performance.

Also the partition alignment makes huge diffrences between 28MB/s and 250MB/s (by 512byte blocksize).

The values are all the same using diffrent linux distros: CentOS, Fedora 13, Ubuntu, SLES.

I know it must have something to do with the stripe size and scheduler settings such as queue_depth and nr_requests, etc. But I can't see the relation between all this settings.

Is there a crack who can give me a little help getting this done? It would be very helpful especially that we work on this issue more than two weeks, read all the available documentations to this topics and the people from 3ware couln't help us yet.

Thanks in advance.

Roland Kaeser

roli8200

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LEARN ABOUT OSF1

stripe

stripe(8)						      System Manager's Manual							 stripe(8)

NAME

       stripe - Stripes a file across several volumes in a file domain

SYNOPSIS

       /usr/sbin/stripe -n  volume_count filename

OPTIONS

       Specifies the number of volumes the striped file crosses. The number of volumes must be greater than one.

OPERANDS

       Specifies the name of the file to stripe.

DESCRIPTION

       The  stripe utility enables you to improve the read/write performance of a file. The stripe utility directs a zero-length file (a file with
       no data written to it yet) to be spread evenly across several volumes within a file domain.  As data is appended to the file, the  data	is
       spread across the volumes. AdvFS determines the number of pages per stripe segment and alternates the segments among the disks in a sequen-
       tial pattern.

       Existing, nonzero-length files cannot be striped using the stripe utility. To stripe an existing file, create a new file,  use  the  stripe
       utility	to  stripe  the  new file, and copy the contents of the file you want to stripe into the new striped file. After copying the file,
       delete the nonstriped file.

       Once a file is striped, you cannot use the stripe utility to modify the number of disks that a striped file crosses. To change  the  volume
       count of a striped file, you can create a second file with a new volume count, and then copy the contents of the first file into the second
       file. After copying the file, delete the first file.

RESTRICTIONS

       You cannot stripe a nonzero-length file or a file that is already striped.

EXAMPLES

       The following example stripes the file abc across three volumes in the same file domain: # stripe -n 3 abc The following example stripes an
       existing,  nonzero-length  file,  foo, across three volumes in the same domain. First a new file, newfoo, is created and striped. Then, the
       contents of file foo are copied to the new, striped file: # touch newfoo # stripe -n 3 newfoo # cp foo newfoo

SEE ALSO

       advfs(4), showfile(8)

																	 stripe(8)