On Fri, Mar 23, 2018 at 5:53 PM, Nicolas Huillard <nhuillard@xxxxxxxxxxx> wrote:
> Le vendredi 23 mars 2018 à 12:14 +0100, Ilya Dryomov a écrit :
>> On Fri, Mar 23, 2018 at 11:48 AM, <ceph@xxxxxxxxxxxxxx> wrote:
>> > The stock kernel from Debian is perfect
>> > Spectre / meltdown mitigations are worthless for a Ceph point of
>> > view,
>> > and should be disabled (again, strictly from a Ceph point of view)
>
> I know that Ceph itself don't need this, but the cpeh client machines,
> specially those hosting VMs or mùore diverse code, should have those
> mitigations.
>
>> > If you need the luminous features, using the userspace
>> > implementations
>> > is required (librbd via rbd-nbd or qemu, libcephfs via fuse etc)
>
> I'd rather use the faster kernel cephfs implementation instead of fuse,
> specially with the Meltdown PTI mitigation (I guess fuse implies twice
> the userland-to-kernel calls which are costly using PTI).
> I don't have an idea yet re. RBD...
>
>> luminous cluster-wide feature bits are supported since kernel 4.13.
>
> This means that there are differences between 4.9 and 4.14 re. Ceph
> features. I know that quota are not supported yet in any kernel, but I
> don't use this...
luminous cluster-wide features include pg-upmap, which in concert with
the new mgr balancer module can provide the perfect distribution of PGs
accross OSDs, and some other OSD performance and memory usage related
improvements.
> Are there some performance/stability improvements in the kernel that
> would justify using 4.14 instead of 4.9 ? I can't find any list
> anywhere...
> Since I'm building a new cluster, I'd rather choose the latest software
> from the start if it's justified.
>From the point of view of the kernel client, a number of issues get
fixed in every kernel release, but only a handful of most important
patches get backported.
Given that 4.14 is available in your environment, there is really no
reason to use 4.9, whether you are starting from scratch or not.
Thanks,
Ilya
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