I came across an enterprise NVMe used for BlueFS DB whose performance dropped sharply after a few months of delivery (I won't mention the brand here but it was not among these 3: Intel, Samsung, Micron). It is clear that enabling bdev_enable_discard impacted performance, but this option also saved the platform after a few days of discard. IMHO the most important thing is to validate the behavior when there has been a write to the entire flash media. But this option has the merit of existing. it seems to me that the ideal would be not to have several options on bdev_*discard, and that this task should be asynchronous and with the (D)iscard instructions during a calmer period of activity (I do not see any impact if the instructions are lost during an OSD reboot) Le ven. 1 mars 2024 à 19:17, Igor Fedotov <igor.fedotov@croit.io> a écrit :
I played with this feature a while ago and recall it had visible negative impact on user operations due to the need to submit tons of discard operations - effectively each data overwrite operation triggers one or more discard operation submission to disk.
And I doubt this has been widely used if any.
Nevertheless recently we've got a PR to rework some aspects of thread management for this stuff, see https://github.com/ceph/ceph/pull/55469
The author claimed they needed this feature for their cluster so you might want to ask him about their user experience.
W.r.t documentation - actually there are just two options
- bdev_enable_discard - enables issuing discard to disk
- bdev_async_discard - instructs whether discard requests are issued synchronously (along with disk extents release) or asynchronously (using a background thread).
Thanks,
Igor
On 01/03/2024 13:06, jsterr@proxforge.de wrote:
Is there any update on this? Did someone test the option and has performance values before and after? Is there any good documentation regarding this option? _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
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