On Fri, 2020-06-05 at 13:02 -0700, Samuel Sieb wrote:
> On 6/5/20 4:25 AM, Patrick O'Callaghan wrote:
> > On Thu, 2020-06-04 at 23:15 +0100, Patrick O'Callaghan wrote:
> > > > The ancient standard is "- - -" and has worked whenever I have used
> > > > it, but google may be able to confirm.
> > >
> > > OK, thanks.
> >
> > Right, that seems to work, however when I bring the drives back online
> > they now have different numbers than before. I would need to know how
> > to keep the previous numbers, or to re-enable the RAID array using the
> > new numbers instead of the old ones.
>
> You don't need an mdadm.conf file or anything. The mdraid system will
> automatically build an array when it sees the drives appear. And if you
> are using UUIDs in any mount descriptions, that will automatically work
> as well.
That doesn't seem to be what's happening:
1) Starting from a fresh reboot, with the array unmounted but active
according to mdadm, I make it inactive:
# echo inactive > /sys/block/md127/md/array_state
(At this point I can make it active again using "echo active ...")
2) I now delete the component drives:
# echo 1 > /sys/block/sdd/device/delete
# echo 1 > /sys/block/sde/device/delete
After a timeout, the drives spin down. So far so good.
3) To spin them up again, I do:
# echo "- - -" > /sys/class/scsi_host/host6/scan
They come up with different numbers (/dev/sd[fg])
However the md system does not detect them:
# mdadm -A
mdadm: an md device must be given in this mode
This contradicts the mdadm man page:
Assemble
Assemble the components of a previously created array into an active array. Components can be explicitly given or can be searched for. mdadm checks that the components do form a bona fide
array, and can, on request, fiddle superblock information so as to assemble a faulty array.
# mdadm -A /dev/md127
mdadm: /dev/md127 not identified in config file. <---- there is no config file
# echo active > /sys/block/md127/md/array_state
-bash: echo: write error: Input/output error
because it's still pointing at the old numbers:
# ls -ld /sys/block/md127/md/dev-*
drwxr-xr-x. 2 root root 0 Jun 5 22:05 /sys/block/md127/md/dev-sdd
drwxr-xr-x. 2 root root 0 Jun 5 22:05 /sys/block/md127/md/dev-sde
It's very possible (indeed likely) that I'm stopping the array in the
wrong way, but I don't see any other way to do it. The mdadm man page
mentions '-A' as the way to start an array, but doesn't talk about how
to stop it, so it could just be leaving out-of-date status information
around and that's what's confusing it.
poc
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