Am Tue, 9 Feb 2016 01:42:40 +0000 (UTC) schrieb Duncan <1i5t5.duncan@xxxxxxx>: > Tho I'd consider benchmarking or testing, as I'm not sure btrfs raid1 > on spinning rust will in practice fully saturate the gigabit > Ethernet, particularly as it gets fragmented (which COW filesystems > such as btrfs tend to do much more so than non-COW, unless you're > using something like the autodefrag mount option from the get-go, as > I do here, tho in that case, striping won't necessarily help a lot > either). > > If you're concerned about getting the last bit of performance > possible, I'd say raid10, tho over the gigabit ethernet, the > difference isn't likely to be much. If performance is an issue, I suggest putting an SSD and bcache into the equation. I have very nice performance improvements with that, especially with writeback caching (random write go to bcache first, then to harddisk in background idle time). Apparently, afaik it's currently not possible to have native bcache redundandancy yet - so bcache can only be one SSD. It may be possible to use two bcaches and assign the btrfs members alternating to it - tho btrfs may decide to put two mirrors on the same bcache then. On the other side, you could put bcache on lvm oder mdraid - but I would not do it. On the bcache list, multiple people had problems with that including btrfs corruption beyond repair. On the other hand, you could simply go with bcache writearound caching (only reads become cached) or writethrough caching (writes go in parallel to bcache and btrfs). If the SSD dies, btrfs will still be perfectly safe in this case. If you are going with one of the latter options, the tuning knobs of bcache may help you actually cache not only random accesses to bcache but also linear accesses. It should help to saturate a gigabit link. Currently, SANdisk offers a pretty cheap (not top performance) drive with 500GB which should perfectly cover this usecase. Tho, I'm not sure how stable this drive works with bcache. I only checked Crucial MX100 and Samsung Evo 840 yet - both working very stable with latest kernel and discard enabled, no mdraid or lvm involved. -- Regards, Kai Replies to list-only preferred. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
