On Thu, May 4, 2023 at 11:35 AM Chris Palmer <[email protected]> wrote:
>
> Hi
>
> Grateful if someone could clarify some things about CephFS Scrubs:
>
> 1) Am I right that a command such as "ceph tell mds.cephfs:0 scrub start
> / recursive" only triggers a forward scrub (not a backward scrub)?
The naming here that has become conventional is unfortunate. Forward
scrub really just means metadata scrub. There is no data integrity
checking.
cephfs-data-scan ("backward" scrub) is just attempting to recover
metadata from what's available on the data pool.
To answer your question: yes.
> 2) I couldn't find any reference to forward scrubs being done
> automatically and was wondering whether I should do them using cron? But
> then I saw an undated (but I think a little elderly) presentation by
> Greg Farnum that states that "forward scrub...runs continuously in the
> background". Is that still correct (for Quincy), and if so what controls
> the frequency?
He was probably referring to RADOS scrub. CephFS does not have any
continuous scrub and has no plans to introduce one.
> 3) Are backward scrubs always manual, using the 3 cephfs-data-scan phases?
Technically there are 5 phases with some other steps. Please check:
https://docs.ceph.com/en/latest/cephfs/disaster-recovery-experts/#recovery-from-missing-metadata-objects
> 4) Are regular backward scrubs recommended, or only if there is
> indication of a problem? (With due regard to the amount of time they may
> take...)
cephfs-data-scan should only be employed for disaster recovery.
--
Patrick Donnelly, Ph.D.
He / Him / His
Red Hat Partner Engineer
IBM, Inc.
GPG: 19F28A586F808C2402351B93C3301A3E258DD79D
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