[Linux-PowerEdge] Extremely poor performance with LVM vs. RAW disc

Gregory Gulik ggulik at reachmail.com
Thu Nov 1 15:53:08 CDT 2012

You brought up possible bug so I checked the firmware.
Turns out it wasn't current so I upgraded and rebooted.
I'm still testing but it looks WAY faster.  It looks so much better that 
I'm not trusting my testing methodology.

On 11/1/12 2:53 PM, Tim Small wrote:
> On 01/11/12 18:20, Gregory Gulik wrote:
>> the performance of the LVM based filesystem is many times slower than 
>> the raw partition.
> Given that writes suffer more than reads, I'm guessing that you 
> probably need to force alignment to the underlying RAID stripe size 
> (and/or possibly the hard disk physical sector size if it is other 
> than 512 bytes) when creating the logical volumes.  i.e. at the moment 
> it seems likely that a single write operation is being changed into 
> two reads and two writes.
> BTW if it's a RAID stripe alignment problem, then I believe that the 
> md (linux software) RAID exposes this info to LVM, but the PERC does 
> not make that info available (or lvm doesn't know how to read it).  An 
> enhancement for Dell to carry out perhaps?  That bug must be latent on 
> thousands of Dell systems?
> Tim.
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Gregory Gulik

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