CentOS - Sep 2013 - to lvm or not to lvm - why/when to use lvm

Hi,

I was wondering, why/when it is useful or when should I avoid to use LVM.

I think the big advantage of LVMing is if you modify (rezising, ...)
disk and filesystem layouts "a lot".

Are there any real pros or cons for following situations regarding e.g.
management and speed?

e.g.:

I do have a server system raid for which the disk layout will not
change; e.g. /var /usr /home will not change much in size.

OR

I do have some file storage shares (iscsi raids) up to some TB each on
one big storage device.

Sometimes (e.g. after a server crash) it is useful to remount the
storage to a different server.

Should I use LVM on the iscsi storage volumes?

	Any suggestion and comment is welcome . Regards . G?tz

-- 
G?tz Reinicke
IT-Koordinator

Tel. +49 7141 969 82 420
Fax  +49 7141 969 55 420
E-Mail goetz.reinicke at filmakademie.de

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71638 Ludwigsburg
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Gesch?ftsf?hrer: Prof. Thomas Schadt

----- Original Message -----
| Hi,
| 
| I was wondering, why/when it is useful or when should I avoid to use
| LVM.
| 
| I think the big advantage of LVMing is if you modify (rezising, ...)
| disk and filesystem layouts "a lot".
| 
| Are there any real pros or cons for following situations regarding
| e.g.
| management and speed?

The speed at which you can manage your disk environment through the use of LVM
makes most of the tradeoffs worth while.  Of course, YMMV so you're best to
test.

| e.g.:
| 
| I do have a server system raid for which the disk layout will not
| change; e.g. /var /usr /home will not change much in size.

This isn't so much the issue.  What if *any* partition requirements *do*
change in the future.  LVM can account for that my allowing you flexibility to
make a change should it be required.  Standard partitioning is less flexible in
this regard.
 
| OR
| 
| I do have some file storage shares (iscsi raids) up to some TB each
| on
| one big storage device.
| 
| Sometimes (e.g. after a server crash) it is useful to remount the
| storage to a different server.

Standard caveats apply.  If the Volume Groups or the Logical Volumes are named
the same moving them to another system with similar VGs or LVs can be
problematic.  Same goes for file system labels, albeit both are relatively easy
to fix in such a scenario.

| Should I use LVM on the iscsi storage volumes?

I would find it difficult to find a case where LVM shouldn't be used because
of it's flexibility.  I tend to use full disk LVM (no partitions at all) and
file system labels for mounting and the like (labels match LVs).

lvcreate -L 20G -n csgrad DATA
mkfs.xfs -L csgrad /dev/DATA/csgrad

/etc/fstab
----------

LABEL=csgrad /exports/csgrad xfs defaults 0 0


LVM offers other additional flexibility too in that you can migrate PVs from one
device to another online.  So if you have one iSCSI server that is coming off
support and you are replacing it with another, you can use pvmove to move the
data from one target to another.

-- 
James A. Peltier
Manager, IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 778-782-6573
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices

?A successful person is one who can lay a solid foundation from the bricks
others have thrown at them.? -David Brinkley via Luke Shaw