On Fri, 15 Sep 2017, Two Spirit wrote: > few questions I'm assuming you're talking about CephFS snapshots here: > 1) Is the idea of snapshotting about 100TB of data doable with Ceph? You can snapshot the entire file system (petabytes) if you like. > 2) How long would such a task take? Are we talking seconds, minutes, > hours, days, weeks? Seconds (if that). > 3) what does "stop i/o" mean. Does the filesystem unavailable to the > user during the snapshot time, or is this administratively unavailable > to the user, or does ceph stop io somewhere while in parallel the data > can be read/written to? There's no IO stoppage. Clients essentially mark a barrier in their writeback caches so that previously buffered writes are contained in the snapshot and new writes are not. How long it takes for that data to be flushed and stable/durable on OSDs depends on how big your client caches are, but that does not cause any io stoppage or gap in availability for users of the file system. sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
