[sf-lug] LVM (& restoring, etc.)

[Michael Paoli]

> Date: Mon, 22 Mar 2010 08:11:37 -0800
> From: jim <jim at well.com>
> Subject: Re: [sf-lug] Partition resizing problem
>
>    there are those who like LVM. i, myself, have some
> reservations about LVM, mainly to do with anxieties
> about restoring data if something happens to corrupt
> the LVM system itself.

Restoring with LVM is quite easy if you don't have / (root) filesystem
using LVM - and even if you do it's not all that horribly complex
(rescue/install CD/DVD or other boot media comes in quite handy - but
you probably need that anyway if the former hard drive turned itself
into a pile of e-waste).  And of course, /boot filesystem needs to not
use LVM (at least for grub 2 - I haven't looked into grub 3 yet).  I've
already done LVM restores at least twice due to hard drive failures.

Typical LVM restore scenario (onto bare hard drive):
initial non-LVM bits:
o partition
o restore /boot filesystem (or non-LVM / if one boots from that)

LVM bits:
o if / is LVM, use rescue media to create LVM /, then restore to it,
   be sure to use suitable parameters for the PV(s) and VG for the above,
   if one doesn't have that meta-data handy, examine it via the vg, etc.,
   commands after /etc has been restored (and if one didn't create it
   suitably, adjust if feasible, or repeat and do it again).
o reboot to single user mode onto restored / (one already has at that
   point, from /etc, /bin and /sbin, what one needs to continue LVM
   restore)
o use vgcfgrestore(8), etc. to reinitialize PV partitions for VG use
   (target PVs must not be smaller than the backed up configuration ones
   they're replacing) and activate VG(s)/LV(s).  If / is LVM, don't
   reinitialized PV(s) that it's already using.
o If there are any volumes(/filesystems) ones wants to restore as
   smaller than they were when backed up, this would be the time to
   shrink them (resize volume(s) as desired before creating filesystems,
   etc.)
o initialize lvm volumes as appropriate (e.g. create filesystems,
   reinitialize lvm swap devices, etc.)
o mount filesystems, activate any lvm swap

I didn't cover most all the stuff that's the same with or without LVM
(e.g. restore filesystem data, any md or encrypted device setup steps,
boot loader installation and configuration, etc.).

Although there's a bit of a learning curve with LVM, with LVM one does
have a much more configurable and generally manageable system - e.g.
grow filesystem on the fly - even if there's no free space immediately
following the filesystem's location on disk.

http://www.rawbw.com/~mp/linux/lvm/balug/

Here's are some example LVM setups:

# hostname
vicki
# mount | awk '/boot/;/mapper/'
/dev/mapper/vg00-root on / type ext3 (rw,errors=remount-ro)
/dev/md0 on /boot type ext3 (rw,nosuid,nodev,noatime)
/dev/mapper/vg00-home on /home type ext3 (rw,nosuid,nodev)
/dev/mapper/vg00-usr on /usr type ext3 (rw,nodev,noatime)
/dev/mapper/vg00-var on /var type reiserfs (rw,nosuid,nodev)
/dev/mapper/vg--balug-balug--var--local--balug on /var/local/balug  
type reiserfs (rw,nosuid,nodev)
/dev/mapper/vg--balug-backup on /var/local/balug/backup type reiserfs  
(ro,nosuid,nodev,noatime)
/dev/mapper/vg--sflug-sflug--disk--BACKUP on  
/var/local/sflug/sflug-disk-BACKUP type ext3 (ro,nosuid,nodev)
# cat /proc/swaps
Filename                                Type            Size    Used    
  Priority
/dev/mapper/vg00-swap                   partition       2097144 0       -1
# df -k / /boot /home /usr /var /var/local/balug  
/var/local/balug/backup /var/local/sflug/sflug-disk-BACKUP
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg00-root
                        1032088    287052    692608  30% /
/dev/md0                241036     57135    171457  25% /boot
/dev/mapper/vg00-home
                        2064208    872924   1086428  45% /home
/dev/mapper/vg00-usr   2064208    656796   1302556  34% /usr
/dev/mapper/vg00-var   4194172   3199144    995028  77% /var
/dev/mapper/vg--balug-balug--var--local--balug
                         204788     42376    162412  21% /var/local/balug
/dev/mapper/vg--balug-backup
                       19684768   9565348  10119420  49%  
/var/local/balug/backup
/dev/mapper/vg--sflug-sflug--disk--BACKUP
                         276440    272632         0 100%  
/var/local/sflug/sflug-disk-BACKUP
#

# hostname
balug-sf-lug-v2.balug.org
# mount | awk '{if(NR==1)print;};/boot/;/mapper/'
/dev/sda5 on / type ext3 (rw,errors=remount-ro)
/dev/sda1 on /boot type ext3 (ro,nosuid,nodev,noatime)
/dev/mapper/vg00-home on /home type reiserfs (rw,nosuid,nodev)
/dev/mapper/vg00-usr on /usr type reiserfs (rw,nodev,noatime)
/dev/mapper/vg00-var on /var type reiserfs (rw,nosuid,nodev)
/dev/mapper/vg01-backup on /var/local/tower type reiserfs (rw,nosuid,nodev)
# cat /proc/swaps
Filename                                Type            Size    Used    
  Priority
/dev/mapper/vg00-swap                   partition       1048568 73124   -1
# df -k / /boot /home /usr /var /var/local/tower
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda5               516040    319716    175356  65% /
/dev/sda1               241116     39309    189359  18% /boot
/dev/mapper/vg00-home
                        2097084    983260   1113824  47% /home
/dev/mapper/vg00-usr   2097084    564832   1532252  27% /usr
/dev/mapper/vg00-var   3145628    989848   2155780  32% /var
/dev/mapper/vg01-backup
                       10485436   8524236   1961200  82% /var/local/tower
#

http://www.rawbw.com/~mp/linux/lvm/balug/