Re: Hot adding active disk to RAID1?

On Sat, 2004-02-07 at 12:37, Mike Perry wrote:

Thus spake Mike Perry (mikepery@fscked.org):

quoted

Well, this is probably a FAQ, but I've really looked around..
Does anyone have any experience with using raidreconf for RAID1, or have
a way to hotadd a disk and have it become active, instead of being a
spare?

Ok, in my impatience I grew some balls.. As it turns out, the RAID1
superblock is (seemingly?) independent of the contents of the volume. So
I was able to simply mkraid --force /dev/md0, this time WITH a
failed-disk directive. Once this was done, I was able to mount /dev/md0
right away, no reformatting or anything needed.

Then I hot-added the failed-disk, and it seems to be synching properly.

And also this time the failed-disk wasn't mirrored to immediately either
(ie without the explicit hotadd).. I wonder why that happened the last
time I did this.. Maybe I just miswrote the raidtab on that occasion..
Or possibly the partition type was raid autodetect and after the reboot
the md driver saw this and decided to start mirroring, regardless of
raidtab?

Anyways, sorry for the spam, but I imagine at least one other poor sap
out there will find this useful ;)

I'm that one.
I ended up at the same place but for another reason. I was in a hurry to
build my system and knew that converting a ext3 to raid would cause some
problem because of some extra raid info, so I defined a raid1 with only
one disk. Later I bought the other disk and tried to add it by changing
/etc/raidtab but that did of course not work and it was at this point I
started to actually read the doc...
I saw reference to an old version of mkraid that would reinitialize the
superblock only (--superblock-only) and keep the data, but newer
raidtools doesn't do that. If that been there or some manpage in the
later version describing it a bit clearer I could dear to do mkraid -f
but with all incarnations of the raid software I no longer know what is
safe in my version.

My current state is that I have root mounted as /dev/md0 created with
one disk (/dev/hda5) as disk 0. I have since then added another disk and
partitioned it equal. I now want to add /dev/hdc5 to md0 (was never
mentioned before). If I add that to raidtab as failed-disk and do
"mkraid -f", will I loose anything?

P.S. I also looked at the src for raidreconf.. it in fact only supports
raid0 and 5, and seems to be nice enough to refuse to do anything if you
have a different raid level. So they got that going for them, which is
nice.

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