Linux – How to clone an lvm ext3 partition to a smaller drive

ext3linuxlvm

I have an lvm ext3 partition that is larger than the drive I would like to clone it onto, but is nowhere close to full, so all of the data, itself, would fit.

What would be the best way to clone this drive to the smaller one?

I would prefer to not have to resize the partition first, if possible.

Best Answer

LVM has built-in support for removing disks from volume groups!. No need for weird uses of copy commands or shrinking.

It is unclear if you mean by "partition" a logical volume. Also, when you say that you wish to use the smaller disk do you mean to get rid of the larger one?

Assuming that you want to stop using the larger disk/partition and remove it from the volume group you would have to:

add (pvcreate) the smaller disk/partition to the volume group
move (pvmove) the physical extents away from larger disk/partition. See this
remove (pvremove) the larger disk/partition from the volume group and do what you will with it.

Oh, and get a good backup first.

Related Solutions

Linux – Ubuntu: Resize the root LVM(2?) partition

In general, here's how to resize LVM volumes:

Let's say /mountpoint is on /dev/VolGroup00/mountpoint. You can find this out by checking out /etc/fstab or by running mount -l.

You may also need to resize the actual Physical Volume, depending on your setup. Use pvdisplay to find out if it's big enough, and use pvresize (much like lvresize below) if necessary.

umount /mountpoint
lvresize -L +<HOW MUCH BIGGER> /dev/VolGroup00/mountpoint
e2fsck -f /dev/VolGroup00/mountpoint
resize2fs /dev/VolGroup00/mountpoint <TOTAL SIZE>
mount /mountpoint

This amounts to umounting, resizing the underlying LVM, then resizing the actual ext3 partition.

A few things to be careful of:

Obviously playing with / will be different from a data partition. You may need a boot disk such as Sysrescuecd instead of Doing It Live. Also see Kristof's comment below -- you may actually be able to do this without unmounting /.
lvresize has a few different syntax options, and reducing a logical volume will probably harm the overlaying partition. Consult your local man pages for more information.

Ubuntu – How to minimise the size of an ext3 partition (and its LVM logical volume)

In theory, yes, you can calculate the exact size of the LV required by the filesystem -- when resize2fs does it's thing, it'll print out how many blocks are in use. Unfortunately, getting it slightly wrong results in a broken filesystem, and wasting 100MB of space in exchange for not boning a filesystem is a tradeoff most people are willing to make.

EDIT: At the risk of giving a monkey a machine gun and hosing your filesystems for all time, the following process worked for me on a scratch filesystem:

fsck -f /dev/vg/sizetest
resize2fs -M /dev/vg/sizetest
Take the number of blocks (and the block size) from the "Resizing the filesystem" line of resize2fs, and calculate the number of kilobytes involved by multiplying the block count by the block size in kB:
- "Resizing the filesystem on /dev/vg/sizetest to 119325 (4k) blocks" translates to 119325 * 4 => 477300 (important number for the next step)
lvresize -L477300k vg/sizetest
At this point, if your size isn't right, you are totally and utterly boned -- expanding the filesystem again won't necessarily get you the same blocks back in the same order.
fsck -f /dev/vg/sizetest
Remount the filesystem, note that df shows that the filesystem is 100% full, with 0 blocks available

If this bones your crucially important filesystem, don't tell me, for I shall merely engage in a lengthy "told you so" dance, and nobody wants to see me dance. Trust me on that.

Best Answer

Related Solutions

Linux – Ubuntu: Resize the root LVM(2?) partition

Ubuntu – How to minimise the size of an ext3 partition (and its LVM logical volume)

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