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

Stephen Cousins steve.cousins at maine.edu
Thu Mar 27 18:56:06 CET 2014


I'm following up on this to let you know that it has been identified as a
ZFS sync issue that has been addressed recently. No need to contact
dm-devel.

Thanks for your help.

Steve


On Thu, Mar 20, 2014 at 6:12 PM, Stephen Cousins <steve.cousins at maine.edu>wrote:

> I'm getting mixed results but it is looking like ZFS have something to do
> with the problem afterall.
>
> I tried it with dm-crypt -> XFS -> NFS and I'm not seeing the same lag
> issue. I say mixed results mainly because I've been using rsync to do the
> testing and for some reason rsync has trouble with this setup. It works but
> really slowly. Like around 3 MB/sec over a Gigabit link. If I use "cp -pR"
> then it goes at 60 MB/sec. I use rsync all the time and I've never seen
> this before so it took a while for me to realize that rsync was acting up.
> Anyone run into this before?
>
> I'll bring this to the ZFSonLinux people and see what they say.
>
> Thanks,
>
> Steve
>
>
> On Thu, Mar 20, 2014 at 3:16 PM, Milan Broz <gmazyland at gmail.com> wrote:
>
>> On 03/20/2014 03:48 PM, Stephen Cousins wrote:
>> > 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 dm-crypt.
>>
>> Hi,
>>
>> unfortunately the dmcrypt code in Centos 6.x is not what is upstream
>> kernel (mainly because of per cpu processing changes upstream).
>> (It would be interesting if it is reproducible with upstream kernel,
>> but I guess it is not easy to test...)
>>
>> I am adding cc to dm-devel list, maybe someone there could have some idea
>> how to help here.
>>
>> Milan
>>
>> >
>> > Thanks,
>> >
>> > Steve
>> >
>> >
>> >
>> > -- ________________________________________________________________
>> > Steve Cousins             Supercomputer Engineer/Administrator
>> > Advanced Computing Group            University of Maine System 244
>> > Neville Hall (UMS Data Center)              (207) 561-3574
>> > <tel:%28207%29%20561-3574> Orono ME 04469
>> > steve.cousins at maine.edu <http://maine.edu>
>>
>
>
>
> --
> ________________________________________________________________
>  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
>
>


-- 
________________________________________________________________
 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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