PERC/6i performance : RAID 0 vs RAID 10

John LLOYD jal at mdacorporation.com
Fri Sep 5 11:37:57 CDT 2008


> Message: 3
> Date: Fri, 5 Sep 2008 00:55:48 -0700
> From: "Priyank Patel" <pkpatel.lists at gmail.com>
> Subject: PERC/6i performance : RAID 0 vs RAID 10
> To: linux-poweredge at dell.com
> Message-ID: <f4e12c70809050055wee27b7r89bc0a28dffe8e24 at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Hi,
> We are testing out the write performance of the PERC/6i RAID 
> controller with
> poweredge servers.  Here are some very surprising numbers 
> from dd (with our
> without O_DIRECT does not seem to matter) - using linux 
> kernel - 2.6.20
> 
> ---
...snip...
> ---
> 
> dd results
> 
> RAID 10 :
> Write ~ 276 MBps
> 
> RAID 0 :
> Write ~ 25 MBps
> Read ~ 540 MBps
> 
> Its pretty confusing why the write performance with a RAID 0 
> across 6 disks
> is so dismal.  We have tried using O_DIRECT, thereby getting rid of
> file-system caching effects...
> 
> Any idea whats going on over here ?
> 
> Thanks,
> -pkpatel
> 
> PS : PERC/5i write performance seems to be as expected (we 
> dont have the
> bencharmark numbers for this yet, but there have been no 
> issues so far)

My own testing of a 6/E shows similar results.  RAID 0 is not good on
6/E -- md is much better.  Two disks assembled with mdadm is 120MB/s
write and 123 MB/s read.  (Read normally is faster on disks).  Using the
6/E Raid-0 setting I get as little as 33 MB/sec.  I'm going to complain
to my tech contact, and ask for a fix.  The performance is not in
accordance with the documentation.

FYI this is on RH 5.1 with patches.  The omreport vdisk and mdadm
--detail reports are as follows; the individual disks are "raid-0" by
themselves.

ID                  : 2
Status              : Ok
Name                : p1
State               : Ready
Progress            : Not Applicable
Layout              : RAID-0
Size                : 372.00 GB (399431958528 bytes)
Device Name         : /dev/sde
Type                : SAS
Read Policy         : No Read Ahead
Write Policy        : Write Back
Cache Policy        : Not Applicable
Stripe Element Size : 64 KB
Disk Cache Policy   : Disabled

ID                  : 3
Status              : Ok
Name                : p2
State               : Ready
Progress            : Not Applicable
Layout              : RAID-0
Size                : 372.00 GB (399431958528 bytes)
Device Name         : /dev/sdf
Type                : SAS
Read Policy         : No Read Ahead
Write Policy        : Write Back
Cache Policy        : Not Applicable
Stripe Element Size : 64 KB
Disk Cache Policy   : Disabled

/dev/md2:
        Version : 00.90.03
  Creation Time : Thu Aug 28 12:51:28 2008
     Raid Level : raid0
     Array Size : 780140032 (744.00 GiB 798.86 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Thu Aug 28 12:51:28 2008
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

     Chunk Size : 128K

           UUID : 3d0b2241:9ef301db:476dd429:d8a9605a
         Events : 0.1

    Number   Major   Minor   RaidDevice State
       0       8       65        0      active sync   /dev/sde1
       1       8       81        1      active sync   /dev/sdf1



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