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Re: Replacing/Adding new hard disk to FC5



Claude Jones wrote:
On Mon October 2 2006 7:13 am, Paul Howarth wrote:
Since you used LVM when installing, this should go quite
smoothly.

There should be no problems with the BIOS or compatibility.

You'll need to use your partitioning tool of choice to create a
partition of type "LVM Physical Volume" on the new disk. You
can then create a new physical volume on that partition
(pvcreate), add the physical volume to your existing volume
group (vgextend) and then resize the logical volume(s) that
your Linux filesystem(s) are on (lvextend) to take advantage of
the extra space. You can then resize the filesystem(s)
themselves (resize2fs or ext2online).

If you do a fresh install of FC6 when it comes out, it should
use both disks by default, so it might just be easier to do
that, if you can back up your data somewhere whilst you do it.

Paul: I wonder if you can tell me the following, which is related. What are the advantages of using LVM vs. say, ext3? I came up on this issue recently, and opted, after an earlier not so successful attempt to add to an LVM (due to time pressures and my own lack of knowledge), to partition disks on a new system using ext2 and ext3 only. Recently, I added a 500GB disk to this system, and I just formatted it as ext3 and mounted it under a name ("archive"), in my home directory. Obviously, using this technique doesn't allow for dynamic expansion of capacity for individual folders, but is there any other advantage to LVM besides this? In Windows land, I finally stopped using dynamic discs because they wound up creating more problems than they eventually solved - for example, the Acronis backup package has issues with dealing with dynamic disks. I have encountered similar issues in dealing with LVM volumes when trouble arises on my Linux box - for example, in the tension of troubleshooting a problem, I've several times had problems using the various flavors of live CD's out there to mount my LVM's - any light you can shed on these questions?

I think that the main advantage of LVM is that it's relatively easy to extend the capacity of your existing filesystems. With manual partitioning, you have to decide where exactly you are going to graft your new filesystem on to an existing filesystem structure. So for instance you may find that /var/spool and /var/cache are taking up lots of space and could do with expanding. You might do that by making a new filesystem for /var, moving everything in the existing /var on to the new filesystem and then mounting the new filesystem on /var. But you might also need more space in /usr, which would need a separate new filesystem to be created and mounted in an appropriate place. You might end up using free space elsewhere and adding symlinks from where the space is needed to where it's available. It can all get very messy.

The default LVM setup just uses one big volume for the entire filesystem hierarchy. This has the advantage that whenever you add space to the LVM VG, you can expand the size of the root filesystem and the space is available wherever it's needed. However, extending the root filesystem often needs to be done using the rescue disk, since you may need to unmount it whilst doing the resize.

So the way I usually structure filesystems when I install Linux is partway between the two approaches. I create separate logical volumes for the /, /home, /tmp, /var, /usr, /srv, and swap space areas, with the root filesystem around 1G. I've never needed to expand the root filesystem on a system set up this way; expanding the other filesystems can be done in single user mode if they need to be unmounted, which is a good bit easier than using the rescue disk.

Paul.


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