On Wed, 30 Nov 2016 00:16:48 +0100 Wilson Meier <wilson.me...@gmail.com> wrote:
> That said, btrfs shouldn't be used for other then raid1 as every other > raid level has serious problems or at least doesn't work as the expected > raid level (in terms of failure recovery). RAID1 shouldn't be used either: *) Read performance is not optimized: all metadata is always read from the first device unless it has failed, data reads are supposedly balanced between devices per PID of the process reading. Better implementations dispatch reads per request to devices that are currently idle. *) Write performance is not optimized, during long full bandwidth sequential writes it is common to see devices writing not in parallel, but with a long periods of just one device writing, then another. (Admittedly have been some time since I tested that). *) A degraded RAID1 won't mount by default. If this was the root filesystem, the machine won't boot. To mount it, you need to add the "degraded" mount option. However you have exactly a single chance at that, you MUST restore the RAID to non-degraded state while it's mounted during that session, since it won't ever mount again in the r/w+degraded mode, and in r/o mode you can't perform any operations on the filesystem, including adding/removing devices. *) It does not properly handle a device disappearing during operation. (There is a patchset to add that). *) It does not properly handle said device returning (under a different /dev/sdX name, for bonus points). Most of these also apply to all other RAID levels. -- With respect, Roman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
