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[dm-devel] 2.6 device mapper performance?


I'm not sure I should ask this question here, if this is not the place then
I apologize. I have a home made NAS with Linux. I use evms to create volume,
put xfs on top of it, and then use samba to share it with Windows clients.
When I was using kernel 2.4 with all the needed patches I could get netbench
106Mbps with 4 clients, and 95Mbps with 8 clients. Recently I upgraded the
same hardware to kernel 2.6 (I also upgraded the related application such as
samba, xfs utility, and dmsetup accordingly). Then I ran netbench again and
got 80Mbps with 4 clients, 53Mbps with 8 clients. Which drop almost 80% (95
vs 53) in 8 clients case.

I then  make and mount xfs on another raid5 (which uses the same disk but on
different partitions) and found it got better performance (95Mbps with 4
clients, 85Mbps with 8 clients). In brief:
xfs volume on raid5 md/md1 on sda6/sdb6/sdc6/sdd6 netbench: 95/85Mbps
xfs volume on EVMS volume /dev/evms/volume1 on raid5 md/md3 on
sda8/sdb8/sdc8/sdd8: 80/53Mbps

Do you think the slow down (85 to 53Mbps) was caused by device mapper?
Please advice.


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