Re: raid6 + caviar black + mpt2sas horrific performance

[Robin Hill <robin@robinhill.me.uk>]

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On Wed Mar 30, 2011 at 10:08:23AM +0200, Louis-David Mitterrand wrote:

> Hi,
> 
> I am seeing horrific performance on a Dell T610 with a LSISAS2008 (Dell
> H200) card and 8 WD1002FAEX Caviar Black 1TB configured in mdadm raid6.
> 
> Besides hardware, the other difference between servers is that the
> PE2900's MegaRAID has no JBOD mode so each disk must be configured as a
> "raid0" vdisk unit. On the T610 no configuration was necessary for the
> disks to "appear" in the OS. Would configuring them as raid0 vdisks
> change anything?
> 
Several years ago I ran into a similar issue with a SCSI RAID controller
(may have been LSI MegaRAID, I can't recall now) and found that RAID0
vdisks were substantially faster than running it in JBOD mode. This
wasn't just down to the controller disabling caching/optimisations
either - in JBOD mode the performance was well below that on a non-RAID
controller.

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

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