-----Original Message-----
From: "Robin Hill" <robin@xxxxxxxxxxxxxxx>
Subj: Re: Best way to re-format RAID1 disks
Date: Thu Mar 26, 2009 1:40 pm
Size: 2K
To: "linux-raid@xxxxxxxxxxxxxxx" <linux-raid@xxxxxxxxxxxxxxx>
On Thu Mar 26, 2009 at 12:10:35PM +0100, Federico wrote:
> Hi all,
> I've two disks in RAID1 formatted with reiserfs which, in my system,
> has amazingly poor performance... I want to switch to ext3 and in a
> couple of kernel releases to upgrade to ext4.
> This is my plan:
>
> 1 - Remove one disk from the array
> 2 - Format the removed disk with ext3 filesystem
> 3 - Copy all the data from the degradeted RAID to the newly ext3-formatted disk
> 4 - Create a new degradeted RAID1 with the ext3 disk
> 5 - Modify grub and reconfigure mdadm to boot in the ext3 RAID1 disk.
> 6 - Reboot.
> 7 - Reformat the reiserfs disk
> 8 - Add the formatted disk to the ext3 RAID and start to syncing.
>
> Is there a more easy and failproof method?
> I'm a bit scared to lose same (or all) of my data during the process...
> Thank you for your help :P
>
You've got a lot of steps in the wrong order here. It also sounds like
the array is your root/boot partition? If so, you'll have to do this
all offline, as the copy won't get everything on a running system.
My suggestion would be to firstly make sure you have a working bootable
CD you can do the migration from (and so you can attempt some recovery
if needed) - my choice would be GRML, but pretty much any live CD will
do.
I'd recommend also booting from CD and running some (read-only) disk
checks (badblocks, SMART tests, dd) first to try to reduce the risk of
later disk failure and data loss. If the array _is_ your root device
(or can't be mounted read-only when you're running normally) then you'll
need to do the whole process from the live CD.
Your process is going to be:
1 - Mount the array in read-only mode.
2 - Remove one disk (disk B) from the array (leaving disk A in the
array).
3 - Erase the superblock on disk B.
4 - Create a new (degraded) array containing only disk B.
5 - Format the array as ext3.
6 - Mount the new array in read-write mode.
7 - Copy all the data from the old array to the new one.
8 - Verify the data (i generally use MD5).
9 - Unmount the old array.
10 - Stop the old array.
11 - Erase the superblock on disk A.
12 - Add disk A into the new array.
13 - Update /etc/fstab and /etc/mdadm.conf
14 - Once the sync is complete, update grub (you'll need to rerun the
setup, not just update the menu) and reboot.
Cheers,
Robin
--
___
( ' } | Robin Hill <robin@xxxxxxxxxxxxxxx> |
/ / ) | Little Jim says .... |
// !! | "He fallen in de water !!" |
...............................................
Robin has good stategy, but there is still possibility of catastrophic full data loss, unless you have a way to prevent one of the disks from having a failure or even getting a unrecoverable read or write error.
Is your data and time worth more than $100? if so buy a 3rd disk and do a full backup as step 0.
David
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