On 06/30/2014 09:26 AM, Kostis Fardelas wrote:
Hi,
from my experience both "ceph osd crush reweight" and "ceph osd
reweight" will lead to CRUSH map changes and PGs remapping. So both
commands eventually redistribute data beween OSDs. Is there any good
reason in terms of ceph performance best practices to choose the one
over the other?
The latter wil only change the weight of the OSD and not the weight of
the host, so that will cause slightly less movement of data and it will
only migrate within that host.
Wido
On 26 June 2014 20:05, Gregory Farnum <g...@inktank.com> wrote:
On Thu, Jun 26, 2014 at 7:03 AM, Micha Krause <mi...@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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Wido den Hollander
42on B.V.
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