[dm-crypt] Poor write performance on software raid with 512k chunk size

Dennis Birkholz dennis.birkholz at rwth-aachen.de
Sun Feb 26 13:29:31 CET 2012


Hello together,

i experienced severe performance problems when using a crypt mapping on
a software raid 5 with 512k chunk size. Without a crypt mapping the
write speed was ~100M/sec, with the crypt mapping it had only ~20M/sec.
After is rebuild the raid on the same disks using 64k chunk size, the
write performance with the crypt mapping is now ~90M/sec. I am using a
self compiled 3.2.6 vanilla kernel on a debian squeeze with an AMD
Phenom(tm) II X4 955 processor.

For now reducing the chunk size solved the problem for me but 512k chunk
size was chosen as the default by mdadm so it would be nice to find the
reason for this performance bottleneck.

Greets,
Dennis


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