Re: LVM performance (was: Re: RAID5 to RAID6 reshape?)

[Iustin Pop <iusty@k1024.org>]

On Tue, Feb 19, 2008 at 01:52:21PM -0600, Jon Nelson wrote:
> On Feb 19, 2008 1:41 PM, Oliver Martin
> <oliver.martin@student.tuwien.ac.at> wrote:
> > Janek Kozicki schrieb:
> >
> > $ hdparm -t /dev/md0
> >
> > /dev/md0:
> >   Timing buffered disk reads:  148 MB in  3.01 seconds =  49.13 MB/sec
> >
> > $ hdparm -t /dev/dm-0
> >
> > /dev/dm-0:
> >   Timing buffered disk reads:  116 MB in  3.04 seconds =  38.20 MB/sec
> 
> I'm getting better performance on a LV than on the underlying MD:
> 
> # hdparm -t /dev/md0
> 
> /dev/md0:
>  Timing buffered disk reads:  408 MB in  3.01 seconds = 135.63 MB/sec
> # hdparm -t /dev/raid/multimedia
> 
> /dev/raid/multimedia:
>  Timing buffered disk reads:  434 MB in  3.01 seconds = 144.04 MB/sec
> #

As people are trying to point out in many lists and docs: hdparm is
*not* a benchmark tool. So its numbers, while interesting, should not be
regarded as a valid comparison.

Just my oppinion.

regards,
iustin