[DRBD-user] Asymmetric performance
agx at sigxcpu.org
Fri Mar 24 16:39:38 CET 2006
It seems drbd shows quiet asymmetric performance on "crossmounted"
devices. I have two HP DL385 (server0 and server1) each with two drbd
devices drbd0 and drbd1 synchronized over a dedicated gigabit ethernet
crosslink between them. Server0 has drbd0 mounted and Server1 has drbd1
mounted. When I only write on one drbd device at a time I see
performance numbers consistent with writes on the local filesystem. But
when I write on both devices at the same time (one on server0 and the
other on server1) I always get 3 times as much throughput on drbd0 than
on drb1 (dbench/tiobench).
The problem seems to always be drbd1, it doesn't matter on which server
of the both the device is mounted.
I tried both consistency modes B and C but this doesn't make an actual
difference. I even played with priority groups but that didn't change
Any ideas? Kernel is x86_64 2.6.16-rc6, drbd is 0.7.17.
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