[ceph-users] Difference between "ceph osd reweight" and "ceph osd crush reweight"

Craig Lewis clewis at centraldesktop.com
Thu Jun 26 14:54:42 PDT 2014


Note that 'ceph osd reweight' is not a persistent setting.  When an OSD
gets marked out, the osd weight will be set to 0.  When it gets marked in
again, the weight will be changed to 1.

Because of this 'ceph osd reweight' is a temporary solution.  You should
only use it to keep your cluster running while you're ordering more
hardware.




On Thu, Jun 26, 2014 at 10:05 AM, Gregory Farnum <greg at inktank.com> wrote:

> On Thu, Jun 26, 2014 at 7:03 AM, Micha Krause <micha at krausam.de> wrote:
> > Hi,
> >
> > could someone explain to me what the difference is between
> >
> > ceph osd reweight
> >
> > and
> >
> > ceph osd crush reweight
>
> "ceph osd crush reweight" sets the CRUSH weight of the OSD. This
> weight is an arbitrary value (generally the size of the disk in TB or
> something) and controls how much data the system tries to allocate to
> the OSD.
>
> "ceph osd reweight" sets an override weight on the OSD. This value is
> in the range 0 to 1, and forces CRUSH to re-place (1-weight) of the
> data that would otherwise live on this drive. It does *not* change the
> weights assigned to the buckets above the OSD, and is a corrective
> measure in case the normal CRUSH distribution isn't working out quite
> right. (For instance, if one of your OSDs is at 90% and the others are
> at 50%, you could reduce this weight to try and compensate for it.)
>
> It looks like our docs aren't very clear on the difference, when it
> even mentions them...and admittedly it's a pretty subtle issue!
> -Greg
> Software Engineer #42 @ http://inktank.com | http://ceph.com
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