On 24/03/14 21:52, Marc MERLIN wrote: > On Mon, Mar 24, 2014 at 07:17:12PM +0000, Martin wrote: >> Thanks for the very good summary. >> >> So... In very brief summary, btrfs raid5 is very much a work in progress. > > If you know how to use it, which I didn't know do now, it's technically very > usable as is. The corner cases are in having a failing drive which you can't > hot remove because you can't write to it. > It's unfortunate that you can't just "kill" a drive without umounting, > making the drive disappear so that btrfs can't see it (dmsetup remove > cryptname for me, so it's easy to do remotely), and remounting in degraded > mode. Yes, looking good, but for my usage I need the option to run ok with a failed drive. So, that's one to keep a development eye on for continued progress... >> Question: Is the raid5 going to be seamlessly part of the >> error-correcting raids whereby raid5, raid6, >> raid-with-n-redundant-drives are all coded as one configurable raid? > > I'm not sure I parse your question. As far as btrfs is concerned you can > switch from non raid to raid5 to raid6 by adding a drive and rebalancing > which effectively reads and re-writes all the blocks in the new format. There's a big thread a short while ago about using parity across n-devices where the parity is spread such that you can have 1, 2, and up to 6 redundant devices. Well beyond just raid5 and raid6: http://lwn.net/Articles/579034/ >> Also (second question): What happened to the raid naming scheme that >> better described the btrfs-style of raid by explicitly numbering the >> number of devices used for mirroring, striping, and error-correction? > > btrfs fi show kind of tells you that if you know how to read it (I didn't > initially). What's missing for you? btrfs raid1 at present is always just the two copies of data spread across whatever number of disks you have. A more flexible arrangement is to be able to set to have say 3 copies of data and use say 4 disks. There's a new naming scheme proposed somewhere that enumerates all the permutations possible for numbers of devices, copies and parity that btrfs can support. For me, that is a 'killer' feature beyond what can be done with md-raid for example. Regards, Martin -- 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
