On Mon, May 9, 2016 at 12:19 AM, K.C. Wong <kcwong@xxxxxxxxxxx> wrote:
>
>> As the tip said, you should not use rbd via kernel module on an OSD host
>>
>> However, using it with userspace code (librbd etc, as in kvm) is fine
>>
>> Generally, you should not have both:
>> - "server" in userspace
>> - "client" in kernelspace
>
> If `librbd` would help avoid this problem, then switch to `rbd-fuse`
> should do the trick, right?
>
> The reason for my line of question is that I've seen occasionl freeze
> up of `rbd map` that's resolved by a 'slight tap' by way of an strace.
> There is definitely great attractiveness to not have specialized nodes
> and make every one the same as the next one on the rack.
The problem with placing the kernel client on the OSD node is the
potential deadlock under heavy I/O when memory becomes scarce. It's
not recommended, but people are doing it - if you don't stress your
system too much, it'll never happen.
"rbd map" freeze is definitely not related to the abov. Did the actual
command hang? Could you describe what you saw in more detail and how
did strace help? It could be that you ran into
http://tracker.ceph.com/issues/14737
Thanks,
Ilya
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