Re: High IO Wait with RAID 1

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On Thu Mar 12, 2009 at 10:21:28PM -0500, Ryan Wagoner wrote:

> I'm glad I'm not the only one experiencing the issue. Luckily the
> issues on both my systems aren't as bad. I don't have any errors
> showing in /var/log/messages on either system. I've been trying to
> track down this issue for about a year now. I just recently my the
> connection with RAID 1 and mdadm when copying data on the second
> system.
> 
> Unfortunately it looks like the fix is to avoid software RAID 1. I
> prefer software RAID over hardware RAID on my home systems for the
> flexibility it offers, especially since I can easily move the disks
> between systems in the case of hardware failure.
> 
> If I can find time to migrate the VMs, which run my web sites and
> email to another machine, I'll reinstall the one system utilizing RAID
> 1 on the LSI controller. It doesn't support RAID 5 so I'm hoping I can
> just pass the remaining disks through.
> 
You could also try using software RAID 10 or RAID 5 on the two drives.
Both of these will be effectively the same as a RAID 1 (ISTR you can
actually just update the metadata to convert from a RAID 1 to a RAID 5)
but will use a different code path so should eliminate the issue you're
seeing.  A 2 drive RAID 10 with far layout will also give some read
performance improvements (at the cost of slightly slower writes).

Cheers,
    Robin

-- 
     ___        
    ( ' }     |       Robin Hill        <robin@xxxxxxxxxxxxxxx> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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