Re: [linux-lvm] LVM2 seems to chop performance by 33%

[David Greaves <david dgreaves com>]

Thanks

I'd tried that, but no real change. I started 1t 128k and also tried 
64k, 256k :) (oh, and 1k)

dd if=/dev/video_vg/video_lv of=/dev/null bs=4k count=256k
262144+0 records in
262144+0 records out
1073741824 bytes transferred in 24.130318 seconds (44497624 bytes/sec)

dd if=/dev/md0 of=/dev/null bs=4k count=256k
262144+0 records in
262144+0 records out
1073741824 bytes transferred in 15.404947 seconds (69701105 bytes/sec)

David

PS wait 'til you see what I'm getting through Rieserfs on top of it!
<sigh>
cu:/huge/editing/tmp# time dd if=dummy.deleteme of=/dev/null bs=4k 
count=256k
262144+0 records in
262144+0 records out
1073741824 bytes transferred in 31.627904 seconds (33949193 bytes/sec)
so throughput down by a factor of 2...
but 1 step at a time....

Stuart Harper wrote:

> While doing backups of my LVM2 drive, I've found that setting the DD block 
> size to 4096 greatly improved my performance. Formerly, DDs on my 240G LVM 
> were taking 23hrs to complete with a block size of 512 or 1024. The same 
> volume now takes less than 2 hours with a block size of 4096. Large numbers 
> did not seem to increase DD speed.
>
> On Thursday 10 June 2004 10:25 am, David Greaves wrote:
>  
>
> > 65Mb/s on the raid5 device
> > 44Mb/s on the lv
> >
> > Is this expected?
> >
> > Kernel 2.6.6
> >
> > representative dd's:
> >
> > cu:/huge/editing/tmp# time dd if=/dev/video_vg/video_lv of=/dev/null
> > bs=1024k count=4k
> > David
> >    
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