is the rbd mirror journal replayed on primary after a crash?

[Scheurer François <francois.scheurer@xxxxxxxxxxxx>]

Hello

Short question regarding journal-based rbd mirroring.

▪IO path with journaling w/o cache:

a. Create an event to describe the update
b. Asynchronously append event to journal object
c. Asynchronously update image once event is safe
d. Complete IO to client once update is safe

[cf. https://events.static.linuxfound.org/sites/events/files/slides/Disaster%20Recovery%20and%20Ceph%20Block%20Storage-%20Introducing%20Multi-Site%20Mirroring_0.pdf]

If a client crashes between b. and c., is there a mechanism to replay the IO from the journal on the primary image?

If not, then the primary and secondary images would get out-of-sync (because of the extra write(s) on secondary) and subsequent writes to the primary would corrupt the secondary. Is that correct?

Cheers

Francois Scheurer

--


EveryWare AG
François Scheurer
Senior Systems Engineer
Zurlindenstrasse 52a
CH-8003 Zürich

tel: +41 44 466 60 00
fax: +41 44 466 60 10
mail: francois.scheurer@xxxxxxxxxxxx
web: http://www.everyware.ch

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