Re: partitioning tools for LVM

On Thursday 11 January 2007 13:35, hendrik@xxxxxxxxxxxxxx wrote:
Are there any partitioning tools that happily deal in LVM on RAID?

parter, gparted, fdisk, cfdisk seem not to, as least fron what
documentation I've managed to find for them.

The nature of your question suggests that you don't really understand how
LVM works. Here is a quick primer and some links:

When using LVM, you first need Physical Volues (PVs). These are real
partitions or drives. Some examples would be /dev/hda2 or /dev/sdb. To use
a device as a physical volume, you typically just run pvcreate on it; in
general, you also set it to an "LVM" type partition using fdisk and
friends, but this isn't strictly necessary. Anyway, it will destroy any
existing data on each partition or device you use for a PV. Setting up PVs
is the ONLY time you'll ever use a program like fdisk or parted. For the
rest, you use LVM tools.

After you've created PVs, you will not ever use them directly. Instead, you
group them together into a Volume Group (VG). A VG has a symbolic name you
give to a group of PVs. You create one with vgcreate, e.g. if I wanted to
create a VG called "vgmain" using two PVs I'd created previously, I might
run "vgcreate vgmain /dev/hda2 /dev/sdb". You can also add and remove PVs
on-the-fly later.

*Finally*, you need to create Logic Volumes, which is the whole point of an
LVM system (that's why it's *Logical Volume Management*). These are the
actual volumes that you treat like you used to treat partitions, e.g. put
file systems on them. You create LVs as part of a Volume Group that you've
previously created, and give them symbolic names. You can add, remove, and
resize them using lv* commands. For instance, if I wanted a 500M LV
named "opt", I might run "lvcreate -n opt -L500M vgmain". Now I'd probably
make a filesystem on it with "mkfs.ext3 /dev/vgmain/opt" and put a line in
my fstab like "/dev/vgmain/opt /opt ext3 defaults 0 0". Later, I might add
or remove more LVs, resize them, etc. I can do all of the online, although
obviously the data itself on the LV (e.g. a filesystem) may need to be
unmounted and/or resized first, although most filesystems can at least GROW
online, while mounted.

Anyway, see <http://tldp.org/HOWTO/LVM-HOWTO/> for a more in depth
discussion. You can pretty much ignore anything that talks about "LVM1"
unless you're working with a legacy system. There are also other systems
like EVMS, but LVM2 is pretty much the mainstream.

--
Wesley J. Landaker <wjl@xxxxxxxxxxxxx> <xmpp:wjl@xxxxxxxxxxxxx>
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