ubuntu at tigershaunt.com
Thu May 17 14:40:54 UTC 2007
Ryan Nichols wrote:
> What is the best way to make a RAID 1 set out of my existing system?
> I've got a 320GB Sata Drive and I want to add a 2nd one and make it
> RAID... What is the best way to do this? I want to keep the data intact.
I'm going to paraphrase these commands. I apologize if I make some
slight syntax errors, but I'm sure you'll get through it with a bit of
perseverance :) Always have a backup before you start something like
this, in case something goes wrong.
Lacking any other information, I'm going to assume, for example, that
your current drive has 1 Linux partition, and one swap partition, sda1
and sda2 respectively. Your new drive will be sdb.
First, you need to partition the drive using any partition tool you are
familiar with. fdisk, cfdisk, gparted, qtparted, etc. The partition
that is destined to be your new filesystem must *not* be any larger than
your current sda1. Smaller is ok, but any size difference will just be
wasted space later. Change the partition type to Linux Raid Autodetect
(type FD). While you're in the partition software, you might as well
add a swap partition on the new drive as well.
Use mdadm to create a new Raid 1 Array, with 2 devices, one will be the
newly created sdb1, the other is missing.
mdadm create /dev/md0 -l 1 /dev/sdb1 missing
Add a filesystem to the new md0 device:
Mount the new filesystem
mount /dev/md0 /mnt/target
The next step is to copy your data from your old drive to the new. But
in order to copy all the static devices that are hidden under the Udev
devices, first, we have to move the udev somewhere else.
mount --move /dev /udev
And now to actually copy the data:
cp -ax / /mnt/target
(You can add the -v switch to the cp command if you want to watch the
progress, but this can slow things down considerably on some systems)
When the copy is done, you need to edit the /mnt/target/etc/fstab file
as well as the /mnt/target/boot/grub/menu.lst file. You need to change
the device of the root device in both files to either /dev/md0 or the
UUID of the new filesystem, depending on your preference.
Now enter the Grub Shell, the command is grub
in the grub shell, issue these commands
device (hd0) /dev/sdb
setup (hd0) (hd0,0)
exit (or quit)
If all went well, and neither of us made a mistake, you should now be
able to remove your old drive, and connect the new drive in its place.
Reboot like that to make sure everything works. If the system boots up
as normal, you might also consider running badblocks on your new drive
to make sure there are no bad sectors creeping up.. The next stage will
erase your old hard drive.
badblocks -v /dev/sda
Now connect your old harddrive back in the system so it would be /dev/sdb
Use a partition tool to change the partition type of /dev/sdb1 to FD
Use mdadm to add the partition to your existing md0 device.
mdadm manage /dev/md0 -a /dev/sdb1
This will silently build the RAID mirror you desired in the background.
you can check on the progress by reading the /proc/mdstat file
open the grub shell again and run the exact same commands as before.
This should make your secondary drive bootable, and in theory should
just boot as normal even if you have to remove the failed primary drive.
If you followed my advice and now have a swap partition on both drives,
you'll want to make certain they are both referenced in in your
/etc/fstab with a priority of 0
/dev/sda2 swap swap pri=0 0 0
/dev/sdb2 swap swap pri=0 0 0
(use use UUID's if you prefer) After you reboot, you can verify all
your swaps are working as intending by looking at the /proc/swaps file
Mine looks like this:
Filename Type Size Used Priority
/dev/sda1 partition 626492 64 0
/dev/sdc1 partition 1951856 64 0
The important part is that they are both there and their priorities are
the same. This will cause linux to spread the load evenly between them,
potentially doubling your swap performance.
You can, if you like things neat, now delete the /mnt/target /udev
directories. They have served their purpose and are no longer needed,
but they wont hurt anything by staying there either.
I've done this kind of procedure and/or parts thereof several times, but
I confess, I never realized how complex the whole damn thing is until I
had to type out all the steps. It is, however, relatively easy to
actually do. :)
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