Re: Cluster is empty but it still use 1Gb of data

[David Turner <drakonstein@xxxxxxxxx>]

[1] Here is a ceph starts on a brand new cluster that has never had any pools created or data or into it at all.  323GB used out of 2.3PB. that's 0.01% overhead, but we're using 10TB disks for this cluster, and the overhead is moreso per osd than per TB.  It is 1.1GB overhead per osd. 34 of the osds are pure nvme and the other 255 have collocated DBs with their WAL on flash. 

The used space your string is most likely just osd overhead, but you can double check if there are any orphaned rados objects using up space with a `rados ls`.  Another thing to note is that deleting a pool in ceph is not instant. It goes into garbage collection and is taken care of over time.  Most likely you're just looking at osd overhead, though.

[1]

$ ceph -s
  cluster:
    health: HEALTH_OK

  services:
    mon: 5 daemons, quorum mon1,mon2,mon4,mon3,mon5
    mgr: mon1(active), standbys: mon3, mon2, mon5, mon4
    osd: 289 osds: 289 up, 289 in

  data:
    pools:   0 pools, 0 pgs
    objects: 0 objects, 0 bytes
    usage:   323 GB used, 2324 TB / 2324 TB avail

On Fri, Mar 2, 2018, 6:25 AM Max Cuttins <max@xxxxxxxxxxxxx> wrote:

How can I analyze this?

Il 02/03/2018 12:18, Gonzalo Aguilar Delgado ha scritto:

Hi Max,

No that's not normal. 9GB for an empty cluster. Maybe you reserved some space or you have other service that's taking the space. But It seems way to much for me.

El 02/03/18 a las 12:09, Max Cuttins escribió:

I don't care of get back those space.
I just want to know if it's expected or not.
Because I run several rados bench with the flag --no-cleanup

And maybe I leaved something in the way.

Il 02/03/2018 11:35, Janne Johansson ha scritto:

2018-03-02 11:21 GMT+01:00 Max Cuttins <max@xxxxxxxxxxxxx>:

Hi everybody,

i deleted everything from the cluster after some test with RBD.
Now I see that there something still in use:

  data:
    pools:   0 pools, 0 pgs
    objects: 0 objects, 0 bytes
    usage:   9510 MB used, 8038 GB / 8048 GB avail
    pgs:

Is this the overhead of the bluestore journal/wall?
Or there is something wrong and this should be zero?

People setting up new clusters also see this, there are overhead items and stuff that eat some space

so it would never be zero. At your place, it would seem it is close to 0.1%, so just live with it and move

on to using your 8TB for what you really needed it to be used for.

In almost no case will I think that "if only I could get those 0.1% back and then my cluster would be great

again".

Storage clusters should probably have something like 10% "admin" margins so if ceph warns and

whines at OSDs being 85% full, then at 75% you should be writing orders for more disks and/or more

storage nodes.

At that point, regardless of where the "miscalculation" is, or where ceph manages to waste

9500M while you think it should be zero, it will be all but impossible to make anything decent with it

if you were to get those 0.1% back with some magic command.

 

--

May the most significant bit of your life be positive.

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