Re: [gentoo-user] Extending a partition with LVM on it

[Josh Cepek]

Marc Joliet wrote:
> I recently did some rearranging of my partitions, so that everything
> except / and /boot (they're where my Windows used to be) is on a
> logical volume.

[cut]

> I wasn't sure how big I should make /var and /usr. /opt is that big in
> the event I install some more games. Otherwise /boot is on sda5, the VG
> maindisk on sda6 and the VG multimedia on sdb.

This is one way you can split up the OS from your data.  Another method
that provides you more flexibility in the future is putting the
partitions on both sda and sdb into the same VG.  A nifty feature of
lvcreate is that you can bind a LV to a particular PV, even if there are
multiple PV's in your VG.  This can be used to allow growth of LV's
beyond the size of the PV they initially reside on.

> Now, since Windows was at the beginning of the hard drive, there is a
> huge gap (about 23 GB) between sda5 and sda6.
>
> What I want to know is, how would I go about filling the gap to have a
> single, large partition for maindisk? Gparted wouldn't do it and I
> didn't dare do anything with cfdisk.
>
> For the moment I added a new partition (via cfdisk, that I did dare do)
> that takes up the entire gap and extended maindisk to that. It's not
> what I wanted, but it works. So that puts the VG on both sda6 (new) and
> sda7 (old sda6). So it looks like this now:
>
>> marcec marcec # pvs
>>  PV         VG         Fmt  Attr PSize   PFree
>>  /dev/sda6  maindisk   lvm2 a-    23,22G  23,22G
>>  /dev/sda7  maindisk   lvm2 a-   273,31G 233,38G
>>  /dev/sdb1  multimedia lvm2 a-   149,05G  39,05G
>
>
> Of course, since I didn't do anything else to maindisk, I understand I
> can always remove the partition from LVM via vgreduce and pvremove.

As long as there is no used space between sda6 and the free space you
have you can expand sda6 to use the extra free space without loosing the
data on the partition.  If you want to go this route, don't forget to
take sda7 out of the VG and pvremove it before deleting it (which is
required if you want to expand sda6 to use all the space)

Before doing this I'd recommend you save a copy of the following
information in the event that you make a typo and need to re-do the
partition sizes:
	fdisk -l /dev/sda; fdisk -lu /dev/sda
Save a copy of that output somewhere safe (ie: NOT on the filesystem
using sda) in the event that you need it.  You shouldn't need this, but
it is a good precaution anyway.  In the event of a problem you can just
re-partition the disk to match this output.

To do this next part you can't be using the partition you wish to
resize, so you will need to boot a rescue environment, such as the
Gentoo Minimal Installation CD or Knoppix.  Once booted, open up fdisk
and delete the sda6 partition (and sda7 if it's not already deleted.)
Then you re-create a new partition in that same location; be sure you
create the new partition with exactly the same starting cylinder as the
old partition, otherwise the data can't be read by LVM.

Next, you need to grow the PV to take advantage of this extra space.  In
most live-CD environments you first need to activate the VG with a
`vgchange -a y VG_NAME` command.  Then issue a `pvresize /dev/sda6` to
grow the PV to the full size if the new partition.  You can confirm this
added the space by checking vgs and pvs for the expected readout.  From
here you're free to grow or add LV's into the new space.


-- 
Josh