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

[David Greaves]

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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