Re: Btrfs and raid5 status with kernel 3.14, documentation, and howto

Marc MERLIN
2014-03-24T21:52:41Z

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.

> 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.

> 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?

Marc
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