Re: [gentoo-user] How to change from one harddrive to software raid

[Joost Roeleveld <joost@antarean.org>]

On Wednesday 30 March 2011 07:28:40 Florian Philipp wrote:
> Am 30.03.2011 05:02, schrieb Einux:
> > Hi,
> > 
> > I bought a new 1T harddrive which is exactly the same as my previous
> > harddrive. So I'm planning to make a Raid-1 layout(for security
> > reasons). But here's the problem: I've already setup LVM2 on the
> > existing harddrive and I don't want to destroy the existing LVM volume
> > groups. I tried to google it, but I'm not sure which is the right
> > keyword. Could you guys help me out?
> > 
> > Thanks in advance:)
> 
> 1. Create a degenerated RAID1 with your new disk
> mdadm --create /dev/md0 --level=1 --raid-devices=2 missing /dev/sdb
> 
> 2. Partition the raid device
> 
> 3. Add one of the partitions to your LVM volume group.
> pvcreate /dev/sdb2
> vgextend volume_group /dev/sdb2
> 
> 4. Move everything from the old physical volumes to the new pv.
> pvmove /dev/sda3 /dev/sdb2
> 
> 5. Remove the old and now empty physical volume
> vgreduce volume_group /dev/sda3
> 
> 6. Move everything else which is not on LVM to your new raid. Guess you
> need to go to single user mode to do this safely.
> 
> 7. Grow your raid to also contain the old disk.
> mdadm /dev/md0 -a /dev/sda
> 
> No, I have not tested this and you should double-check everything. No
> guarantees, etc.
> 
> One warning, though: pvmove is known to create problems from time to
> time. Leaking memory, bogging systems with infinite system load and so
> on. If it gives you trouble, you can abort it with `pvmove --abort` and
> try it again later by calling `pvmove volume_group` (without physical
> device specified) to resume it. It SHOULD survive system crashes.
> Trying another kernel version sometimes helps when pvmove gives you trouble.

To avoid that, with "large" moves, do the following:
# pvmove -i 600 /dev/sda3 

The "-i 600" means, only report every 10 minutes. It's the "reporting" that 
causes the memory leak.

Also, when just wanting to "empty" one physical volume, it is not necessary to 
specify the "target".
It's a good idea to mark the PVs on the existing drive "non-allocatable". Then 
LVM won't try to move anything to that PV:
# pvchange -xn /dev/sda3

The rest of the steps read correct. It's how I did a similar operation, but 
still double-check all the parameters and when in doubt, read the manual 
and/or ask on the list.

--
Joost Roeleveld