On 12/04/2014 05:45 AM, David McGuffey wrote:
md0 is made up of two 250G disks on which the OS and a very large /var
partions resides for a number of virtual machines.
...
Challenge is that disk 0 of md0 is the problem and it has a 524M /boot
partition outside of the raid partition.
Assuming that you have an unused drive port, you can fix that pretty easily.
Attach a new replacement disk to the unused port. Let's say that it
comes up as /dev/sde.
Copy the partition table to it (unless it's GPT, in which case use parted):
sfdisk -d /dev/sda | sfdisk /dev/sde
Unmount /boot and copy that partition (assuming that it is sda1):
umount /boot
dd if=/dev/sda1 of=/dev/sde1 bs=1M
Install grub on the new drive:
grub-install /dev/sde
At that point, you should be able to also add the new partition to the
md array:
mdadm /dev/md0 /dev/sda2
Once it rebuilds, shut down. Remove the bad drive. Put the new drive
in its place. In theory the system will boot and be whole.
In practice, however, there's a bunch of information you didn't provide,
so some of those steps are wrong.
I'm not sure what dm-0, dm-2 and dm-3 are, but they're indicated in your
mdstat. I'm guessing that you made partitions, and then made LVM or
crypto devices, and then did RAID on top of that. If either of those
are correct, that's completely the wrong way to build RAID sets. You
risk either bad performance from doing crypto more often than is
required, or possibly corruption as a result of LVM not mapping blocks
the way you expect.
If you build software RAID, I really strongly recommend that you keep it
as simple as possible. That means a) build sofware RAID sets from raw
partitions and b) use as few partitions as possible.
Typically, I'll create two partitions on all disks. The first is a
small partition for /boot, which may be part of a RAID1 set or may be
unused. The second partition covers the rest of the drive and will be
used in whatever arrangement is suitable for that system, whether it's
RAID1, RAID5, or RAID10. All of the drives are consistent, so there's
always a place to copy /boot, and just one script or process to set up
new disks regardless of their position in the array. md0 is used for
/boot, and md1 is an LVM PV. All of the filesystems other than /boot
are LVs.
Hopefully btrfs will become the default fs in the near future and all of
this will be vastly simplified.
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