On Thu, May 4, 2023 at 11:35 AM Chris Palmer <chris.palmer@idnet.com> 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-f...
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