Re: unbalanced OSDs

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ceph osd reweight-by-utilization <percentage> needs another argument to do something.  The recommended starting value is 120.  Run it again with lower and lower values until you're happy.  The value is a percentage, and I'm not sure what happens if you go below 100.  If you get into trouble with this (too much backfilling causing problems), you can use ceph osd weight <osdid> 1 to go back to "normal", just look at ceph osd tree to see the reweighted osds.

Bear in mind that reweight-by-utilization adjusts the osd weight, which is not a permanent value.  in/out events will reset this weight.

But that's ok, because you don't need the reweight to last very long.  Even if you get it perfectly balanced, you're going to be at ~75%.  I order more hardware when I hit 70% utilization.  Once you start adding hardware, the data distribution will change, so any permanent weights you set will probably be wrong.

If you do want the weights to be permanent, you should look at ceph osd crush reweight <osdid> <weight>.  This permanently changes the weight in the crush map, and it's not affected by in/out events.  Bear in mind that you'll probably have to revisit all of these weights anytime your cluster changes.  Also note that this <weight> is different that ceph osd reweight.  This weight is the disk size in TiB.  I recommend small change to all over and under utilizied disks, then re-evaluate each pass.

On Wed, Apr 22, 2015 at 4:12 AM, Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx> wrote:

i've heavily unbalanced OSDs.

Some are at 61% usage and some at 86%.

Which is 372G free space vs 136G free space.

All are up and are weightet at 1.

I'm running firefly with tunables to optimal and hashpspool 1.

Also a reweight-by-utilization does nothing.

# ceph osd reweight-by-utilization
no change: average_util: 0.714381, overload_util: 0.857257. overloaded
osds: (none)

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