Grow a LVM over software raid with a new harddisk

[Keith Richie]

On Nov 14, 2007 4:29 AM, Owen Townend <bowbowbow at optushome.com.au> wrote:

>
> On Wed, 2007-11-14 at 16:10 +0800, Shu Hung (Koala) wrote:
> > Hello all,
> >
> > Anyone knows how to grow a LVM over software raid with a new harddisk?
> >
> > What I mean is I have a new harddisk. I plugged it in my machine. And
> > now, how do I:
> > (1) add this harddisk to my existing software raid, grow it without
> > affecting files in it
> > (2) grow my LVM volume group accordingly without affecting files in it
> > (3) add the new storage space to a specific lvm without affecting the
> > data in it
> >
> > Is there any way?
> >
> >
> > Thanks,
> > Koala Yeung
>
> Hey,
>
> There is definitely a way!
> In this case the man pages are your friend.
> So long as your setup isn't too exotic it should be fairly straight
> forward. Substitute your devices etc for the ones I've used and read the
> man pages and check options etc before running anything.
>
> There are three stages, grow mdadm, extend lvm and extend the
> filesystem. How each of these is done is dependant on your setup namely
> raid level & filesystem type as well as the use the setup is put to. LVM
> should be able to extend anyway so long as you're using LVM2. (LVM1 had
> some hard limits on sizing that needed to be decided on creation.)
> If this is used as your root partition you'll need to boot a livecd
> distro or rescuecd to access it and allow you to make the changes. Also,
> if you are extending a raid5 array you'll want another device (hdd,
> floppy, usb stick, etc) to store the mdadm backup data it keeps while
> performing the extension.
>
> If it's just a storage array then the expansion should be as easy as
> (for example)
> # mdadm --add /dev/md0 /dev/sdd1
> # mdadm --grow /dev/md0 --raid-devices=4
>
> This can be done online (mounted) if you wish but it'll be slower.
>
> Then wait for a few hours watching /proc/mdstat as something like this
> shows up
> [>....................] reshape = 0.0% (166656/390708736)
> finish=1347.2min speed=4830K/sec
> (from http://scotgate.org/?p=107)
>
> Then let LVM know you've changed the disk
> # pvresize /dev/md0
>
> Next extend the logical volume by the desired amount,
> For example all of the new space:
> # lvextend -l 100%FREE /dev/datavg/datalv
>
> Lastly, extend the filesystem. In my case this is usually reiserfs so:
> The default if no new size is given is to fill the available space.
>
> Unmount if you haven't already
> # umount /dev/datavg/datalv
> # resize_reiserfs /dev/datavg/datalv
> # mount /dev/datavg/datalv
>
> This is similar for ext3:
> # resize2fs /dev/datavg/datalv
>
> Hopefully all done :)
>
> cheers,
> Owen.
>
>
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Thanks for this Owen. I don't have an LVM setup yet. I was just
contemplating this exact issue yesterday, and was wondering how
easy/difficult it would be to do something like this. Seems so straight
forward, I'd be a fool not to go ahead and set the ground work up on my next
PC build for LVM.
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