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

Tim Small tim at seoss.co.uk
Thu Nov 1 14:53:06 CDT 2012


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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