It seems Discard support for kernel rbd is targeted for v80.. http://tracker.ceph.com/issues/190
Thanks & Regards Somnath -----Original Message----- From: ceph-users-boun...@lists.ceph.com [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of Christian Balzer Sent: Wednesday, April 16, 2014 5:36 PM To: ceph-users@lists.ceph.com Subject: Re: [ceph-users] question on harvesting freed space On Wed, 16 Apr 2014 13:12:15 -0500 John-Paul Robinson wrote: > So having learned some about fstrim, I ran it on an SSD backed file > system and it reported space freed. I ran it on an RBD backed file > system and was told it's not implemented. > > This is consistent with the test for FITRIM. > > $ cat /sys/block/rbd3/queue/discard_max_bytes > 0 > This looks like you're using the kernelspace RBD interface. And very sadly, trim/discard is not implemented in it, which is a bummer for anybody running for example a HA NFS server with RBD as the backing storage. Even sadder is the fact that this was last brought up a year or even longer ago. Only the userspace (librbd) interface supports this, however the client (KVM as prime example) of course need to use a pseudo disk interface that ALSO supports it. The standard virtio-block does not, while the very slow IDE emulation does as well as the speedier virtio-scsi (however that isn't configurable with ganeti for example). Regards, Christian > On my SSD backed device I get: > > $ cat /sys/block/sda/queue/discard_max_bytes > 2147450880 > > Is this just not needed by RBD or is cleanup handled in a different way? > > I'm wondering what will happen to a thin provisioned RBD image > overtime on a file system with lots of file create delete activity. > Will the storage in the ceph pool stay allocated to this application > (the file > system) in that case? > > Thanks for any additional insights. > > ~jpr > > On 04/15/2014 04:16 PM, John-Paul Robinson wrote: > > Thanks for the insight. > > > > Based on that I found the fstrim command for xfs file systems. > > > > http://xfs.org/index.php/FITRIM/discard > > > > Anyone had experiences using the this command with RBD image backends? > > > > ~jpr > > > > On 04/15/2014 02:00 PM, Kyle Bader wrote: > >>> I'm assuming Ceph/RBD doesn't have any direct awareness of this > >>> since the file system doesn't traditionally have a "give back blocks" > >>> operation to the block device. Is there anything special RBD does > >>> in this case that communicates the release of the Ceph storage > >>> back to the pool? > >> VMs running a 3.2+ kernel (iirc) can "give back blocks" by issuing > >> TRIM. > >> > >> http://wiki.qemu.org/Features/QED/Trim > >> > > _______________________________________________ > > ceph-users mailing list > > ceph-users@lists.ceph.com > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Christian Balzer Network/Systems Engineer ch...@gol.com Global OnLine Japan/Fusion Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com ________________________________ PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify the sender by telephone or e-mail (as shown above) immediately and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies). _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
