To be pedantic … backfill usually means copying data in toto, so like normal write replication it necessarily has to traverse the WAN. Recovery of just a lost shard/replica in theory with the LRC plugin, but as noted that doesn’t seem like a good choice. With the default EC plugin, there *may* be some read locality preference but it’s not something I would bank on. Stretch clusters are great when you need zero RPO when you really need a single cluster and can manage client endpoint use accordingly. But with tradeoffs, in many cases two clusters with async replication can be a better solution, depends on needs and what you’re solving for. > On May 7, 2025, at 5:06 AM, Janne Johansson <icepic.dz@xxxxxxxxx> wrote: > > Den ons 7 maj 2025 kl 10:59 skrev Torkil Svensgaard <torkil@xxxxxxxx>: >> We are looking at a cluster split between two DCs with the DCs as >> failure domains. >> >> Am I right in assuming that any recovery or backfill taking place should >> largely happen inside each DC and not between them? Or can no such >> assumptions be made? >> Pools would be EC 4+8, if that matters. > > Unless I am mistaken, the first/primary of each PG is the one "doing" > the backfills, so if the primaries are evenly distributed between the > sites, the source of all backfills would be in the remote DC in 50% of > the cases. > I do not think the backfills are going to calculate how it can use > only "local" pieces to rebuild a missing/degraded PG piece without > going over the DC-DC link even if it is theoretically possible. > > -- > May the most significant bit of your life be positive. It’s good to be 8-bit-clean, if you aren’t , then Kermit can compensate. > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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