[dm-crypt] trouble with dm-crypt and NFS: server hangs

Stephen Cousins steve.cousins at maine.edu
Thu Mar 20 15:48:52 CET 2014

I am testing dm-crypt with a system that serves data over NFS. I'm finding
that when serving the data over NFS4 it will go for a little while and then
it will just stop copying and networking on the NFS server will stall out
so that other connections to other parts of the storage (a non-dm-crypt
volume) will become very laggy. Soon after canceling the copy the other
connections resume back to normal.

I have tried this on two different servers, one with a single disk with ZFS
and another with a ZFS raidz2 pool and they both do the same thing. CPU
doesn't seem to be an issue. Doing local copies is not a problem. That is,
copying to/from these volumes made up of dm-crypted disks from other disks
on the server have no problems.

One system (the one with the RAID pool) is CentOS 6.4 and the other one is
CentOS 6.5.

I'm curious if anyone else has run into this before and if so, what can be
done to make it work? I'm going to test to see if taking ZFS out of the
equation helps. I haven't run into this with ZFS with disks without



 Steve Cousins             Supercomputer Engineer/Administrator
 Advanced Computing Group            University of Maine System
 244 Neville Hall (UMS Data Center)              (207) 561-3574
 Orono ME 04469                      steve.cousins at maine.edu
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