David Woodhouse wrote:
On Mon, 2009-07-13 at 12:28 +0200, Tomasz Chmielewski wrote:
How do I replace failed disks in RAID-1 mode?
I don't think you can. In theory you can remove the broken one, and you
can add a _new_ empty one -- I say 'in theory' because you seem to have
demonstrated both of those actions failing.
But I don't believe we have yet implemented anything to let you
_replace_ a failed disk and recreate its original contents.
I had that on my TODO list for some time after I get the basic RAID[56]
operation working.
It would be also interesting to have a tool to monitor the state of the
RAID (i.e. similar to what /proc/mdstat provides for md).
I also tried to compare what happens when we do writes to md-raid and to
btrfs-raid (RAID-1 in both cases) and it looks... strange for btrfs. Or
perhaps this is how RAID-1 works in btrfs?
I used iostat to monitor the writes on both devices.
With md RAID-1, when we do:
# dd if=/dev/zero of=/mnt/md-raid-1/testfile
and
# iostat -dk 1
We can see the write speed on both devices is more or less the same.
With btrfs RAID-1, when we do the same, I can see that writes go to one
drive, while the second drive receives 0 kb/s writes; then it changes
(one drive is written to, the second isn't). Only sometimes, writes
happen concurrently to both drives, like with md RAID-1.
Is it intended?
--
Tomasz Chmielewski
http://wpkg.org
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