Molle Bestefich wrote:
On 7/8/05, Neil Brown <neilb@xxxxxxxxxxxxxxx> wrote:
On Thursday July 7, molle.bestefich@xxxxxxxxx wrote:
Mitchell Laks wrote:
However I think that raids should boot as long as they are intact, as a matter
of policy. Otherwise we lose our ability to rely upon them for remote
servers...
It does seem wrong that a RAID 5 starts OK with a disk missing, but a
RAID 1 fails.
Perhaps MD is unable to tell which disk in the RAID 1 is the freshest
and therefore refuses to assemble any RAID 1's with disks missing?
This doesn't sound right at all.
"--run" is required to start a degraded array as a way of confirming
to mdadm that you really have listed all the drives available.
The normal way of starting an array at boot time is by describing the
array (usually by UUID) in mdadm.conf and letting mdadm find the
component devices with "mdadm --assemble --scan".
This usage does not require --run.
The only time there is a real reluctance to start a degraded array is
when it is raid5/6 and it suffered an unclean shutdown.
A dirty, degraded raid5/6 can have undetectably data corruption, and I
really want you to be aware of that and not just assume that "because
it started, the data must be OK".
Sounds very sane.
So a clean RAID1 with a disk missing should start without --run, just
like a clean RAID5 with a disk missing?
Nevermind, I'll try to reproduce it instead of asking too many questions.
And I suck a bit at testing MD with loop devices, so if someone could
pitch in and tell me what I'm doing wrong here, I'd appreciate it very
much (-:
# mknod /dev/md0 b 9 0
# dd if=/dev/zero of=test1 bs=1M count=100
# dd if=/dev/zero of=test2 bs=1M count=100
# dd if=/dev/zero of=test3 bs=1M count=100
# losetup /dev/loop1 test1
# losetup /dev/loop2 test2
# losetup /dev/loop3 test3
# mdadm --create /dev/md0 -l 1 -n 3 /dev/loop1 /dev/loop2 /dev/loop3
mdadm: array /dev/md0 started.
# mdadm --detail --scan > /etc/mdadm.conf
# cat /etc/mdadm.conf
ARRAY /dev/md0 level=raid1 num-devices=3
UUID=1dcc972f:0b856580:05c66483:e14940d8
devices=/dev/loop/1,/dev/loop/2,/dev/loop/3
Why does this show /dev/loop/1 instead of /dev/loop1 ?
# mdadm --stop /dev/md0
# mdadm --assemble --scan
mdadm: no devices found for /dev/md0
// ^^^^^^^^^^^^^^^^^^^^^^^^ ??? Why?
# mdadm --assemble /dev/md0 /dev/loop1 /dev/loop2 /dev/loop3
mdadm: /dev/md0 has been started with 3 drives.
// So far so good..
# mdadm --stop /dev/md0
# losetup -d /dev/loop3
# mdadm --assemble /dev/md0 /dev/loop1 /dev/loop2 /dev/loop3
mdadm: no RAID superblock on /dev/loop7
mdadm: /dev/loop7 has no superblock - assembly aborted
Where's loop7 coming from all of a sudden? I thought you were using
loop1, loop2, loop3
// ^^^^^^^^^^^^^^^^^^^^^^^^ ??? It aborts :-(...
// Doesn't an inactive loop device seem the same as a missing disk to MD?
# rm -f /dev/loop3
# mdadm --assemble /dev/md0 /dev/loop1 /dev/loop2 /dev/loop3
mdadm: cannot open device /dev/loop7: No such file or directory
mdadm: /dev/loop7 has no superblock - assembly aborted
Once again, where is loop7 coming from?
// ^^^^^^^^^^^^^^^^^^^^^^^^ ??? It aborts, just as above...
Hm!
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