On Tue, May 12, 2015 at 8:37 PM, Chad William Seys
<cwseys@xxxxxxxxxxxxxxxx> wrote:
> Hi Ilya and all,
> Is it safe to use kernel 3.16.7 rbd with Hammer tunables? I've tried
> this on a test Hammer cluster and the client seems to work fine.
> I've also mounted cephfs on a Hammer cluster (and Hammer tunables) using
> kernel 3.16. It seems to work fine (but not much testing). I remember
> recently someone asking about mounting cephfs with Hammer tunables and it was
> stated that kernel 4.1 was needed for mounting.
> Is the more correct statement that mounting is possible but problems will
> exist?
Any kernel is safe to use with hammer release, although the later the
kernel is the more kernel client bug fixes it has. As far as tunables,
hammer tunables are the same as firefly, except when it comes to
*building* crush maps. So if you build your crushmap with firefly
tunables and then enable hammer tunables, nothing is going to happen
and you will still be able to use kernels 3.15 and above (firefly
tunables are supported starting with 3.15).
However if you actually build (or make modifications to) your crushmap
with hammer tunables enabled, it will most certainly use the new straw2
buckets instead of the old straw buckets and *that* requires kernel
4.1. You wouldn't be able to mount 3.16 with straw2 buckets in your
crushmap, so it's all safe.
Thanks,
Ilya
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