On Fri, Oct 27, 2017 at 6:33 PM, Bogdan SOLGA <bogdan.solga@xxxxxxxxx> wrote:
> Hello, everyone!
>
> We have recently upgraded our Ceph pool to the latest Luminous release. On
> one of the servers that we used as Ceph clients we had several freeze
> issues, which we empirically linked to the concurrent usage of some I/O
> operations - writing in an LXD container (backed by Ceph) while there was an
> ongoing PG rebalancing. We searched for the issue's cause through the logs,
> but we haven't found anything useful.
What kind of freezes -- temporary slowdowns or hard lockups? Did they
resolve on their own or did you have to intervene?
>
> At that time the server was running Ubuntu 16 with a 4.5 kernel. We thought
> an upgrade to the latest HWE kernel (4.10) would help, but we had the same
> freezing issues after the kernel upgrade. Of course, we're aware that we
> have tried to fix / avoid the issue without understanding it's cause.
>
> After seeing the OS recommendations from the Ceph page, we reinstalled the
> server (and got the 4.4 kernel), we ran into a feature set mismatch issue
> when mounting a RBD image. We concluded that the feature set requires a
> kernel > 4.5.
>
> Our question - how would you recommend us to proceed? Shall we re-upgrade to
> the HWE kernel (4.10) or to another kernel version? Would you recommend an
> alternative solution?
The OS recommendations page lists upstream kernels, as a general
guidance. As long as the kernel is fairly recent and maintained
(either upstream or by the distributor), it should be fine. 4.10 is
certainly better than 4.4-based kernels, at least for the kernel
client.
Thanks,
Ilya
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