Hallo all,
I am not sure RBD discard is working in my setup, and I am asking for your help.
    (I searched this mailing list for related messages and found one by
    Nathan Harper last 29th Jan 2018 "Debugging fstrim issues" which
    however mentions trimming was masked by logging... so I am not 100%
    sure of what is the expected result)

I am on Ocata, and Ceph 10.2.10.
Followed the recipe: https://www.sebastien-han.fr/blog/2015/02/02/openstack-and-ceph-rbd-discard/
 * setup Nova adding to /etc/nova/nova.conf
...
[libvirt]
hw_disk_discard = unmap
...
* decorated a CentOS image with hw_scsi_model=virtio--scsi,hw_disk_bus=scsi
 * created a VM with boot disk on Ceph (my default is ephemeral,
   though), verified the XML shows my disk is scsi,


I see that commands:
rbd --cluster cephpa1 diff cinder-ceph/${theVol} | awk '{ SUM += $2 } END { print SUM/1024/1024 " MB" }' ; rados --cluster cephpa1 -p cinder-ceph ls | grep rbd_data.{whatever} | wc -l show the size increases but does not decrease when I execute delete the temporary file and execute
        sudo fstrim -v /

  Am I missing something?

I do see that adding/removing files created with dd does not always result in a global size increase, it is as if the dirty blocks are kept around and reused. Is this the way discard is supposed to work?

  Thanks for your help!

                        Fulvio

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