Re: mdadm -homehost problem [SOLVED]
On Tue, 2012-09-04 at 11:45 -0700, Ross Boylan wrote:
> Summary: mdadm on squeeze rewrites the UUID I give it with the
> localhost, even if I do not specify localhost. I am trying to repair a
> RAID for use on lenny with an existing UUID. Is there a way to avoid
> the rewrite? Other solutions?
>
> Details
>
> A lenny host has two virtual machines, VM1 (lenny) and VM2 (squeeze).
> There are two virtual disks, VD0 and VD1, whose 3rd partition forms
> RAID1 (md1), intended for VM1. That same partition was in a RAID
> before, but I grew it and so there is no RAID superblock near the end
> anymore. I need to recreate the superblock without zapping the good data
> on the partition.
>
> >From VM2:
> # mdadm --create /dev/md1 --uuid=6f05ff4e:b4d49c1f:7fa21d88:ad0c50a9
> --metadata=0.90 --level=mirror --raid-devices=2 /dev/sdb3 missing
> mdadm: array /dev/md1 started.
> # mdadm --examine /dev/sdb3
> /dev/sdb3:
> Magic : a92b4efc
> Version : 0.90.00
> UUID : 6f05ff4e:b4d49c1f:f1c4dd81:d9ca9b38 (local to host
> squeeze00)
>
> The man appears to say the UUID specified on the command line should
> govern(*), but it doesn't.
>
> Some possible fixes:
[snip]
> 4) Find an appropriate rescue system image for lenny, start it in a VM,
> and run mdadm from there. I wonder if stopping VM1's startup while it's
> still in the initrd would be enough.
The last option worked, with some work.
I booted into the lenny VM specifying break=mount. At the prompt I had
to do "modprobe md" to get things to work; then mdadm --create wrote the
new superblock. Because the underlying partitions were out of sync, I
created raid1 with only 1 of the partitions, and then added in the
other. After it synced I restarted the VM and the newly expanded md1
was there.
For the record, md1 was a physical volume for LVM. So the complete
sequence was to then
pvresize /dev/md1 # makes the PV fill the whole md1
lvextend -L+1G myvg/usr # grow an LV that needed more room
resize2fs /dev/myvg/usr # online resize of filesystem
Although mdadm has some commands for --grow'ing the size of the md, I
did not need to use any of them. Possibly that's because I used RAID1.
Ross
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