linux - LVM mount physical disk for backups

27
2013-07

Romski

I have a home server running Centos 6.4. There are 2 400GB physical disks, and I believe I have 1 logical volume over one of the disks. I want to mount the 2nd disk under /backup and use it for backups only (my thinking was to keep backup data on a separate physical device).

Are my assumptions about my set up correct?
Should I add the 2nd disk to the LVM, and if so how do I ensure that only backup data goes to the 2nd disk?
Should I the disk some other way

I've included some paired down output that I hope will be useful:

[root@server ~]# fdisk -l

Disk /dev/sda: 400.1 GB, 400088457216 bytes
...

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              64       48642   390198272   8e  Linux LVM

Disk /dev/sdb: 400.1 GB, 400088457216 bytes
...

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1       48642   390710272   83  Linux

Disk /dev/mapper/vg_server-lv_root: 53.7 GB, 53687091200 bytes
... 

Disk /dev/mapper/vg_server-lv_swap: 8405 MB, 8405385216 bytes
...

Disk /dev/mapper/vg_server-lv_home: 337.5 GB, 337469505536 bytes
...

[root@server ~]# df -H
Filesystem             Size   Used  Avail Use% Mounted on
/dev/mapper/vg_server-lv_root
                        53G   3.5G    47G   7% /
tmpfs                  4.2G      0   4.2G   0% /dev/shm
/dev/sda1              508M    68M   415M  14% /boot
/dev/mapper/vg_server-lv_home
                       333G    41G   275G  13% /home

[root@server ~]# pvs --all
  PV                     VG        Fmt  Attr PSize   PFree
  /dev/ram0                             ---       0     0
  /dev/ram1                             ---       0     0
  /dev/ram10                            ---       0     0
  /dev/ram11                            ---       0     0
  /dev/ram12                            ---       0     0
  /dev/ram13                            ---       0     0
  /dev/ram14                            ---       0     0
  /dev/ram15                            ---       0     0
  /dev/ram2                             ---       0     0
  /dev/ram3                             ---       0     0
  /dev/ram4                             ---       0     0
  /dev/ram5                             ---       0     0
  /dev/ram6                             ---       0     0
  /dev/ram7                             ---       0     0
  /dev/ram8                             ---       0     0
  /dev/ram9                             ---       0     0
  /dev/root                             ---       0     0
  /dev/sda1                             ---       0     0
  /dev/sda2              vg_server lvm2 a--  372.12g    0
  /dev/sdb1                             ---       0     0
  /dev/vg_server/lv_home                ---       0     0
  /dev/vg_server/lv_swap                ---       0     0

Edit

Further output as requested

[root@server ~]# cat '/proc/partitions'
major minor  #blocks  name

   8        0  390711384 sda
   8        1     512000 sda1
   8        2  390198272 sda2
   8       16  390711384 sdb
   8       17  390710272 sdb1
 253        0   52428800 dm-0
 253        1    8208384 dm-1
 253        2  329560064 dm-2

Answers

psusi

You appear to have 3 logical volumes: root, /home, and swap. There's no reason to add the backup drive to LVM. If you do, then you can specify which disk a volume should be allocated on when you create it, though in your case, your first disk is already 100% allocated, so the new disk is the only place a new volume could go.

Related Answers

Sathya

Faced this problem a while ago, I'd posted this on my blog

List out all your partitions, type

linux:/ # lvmdiskscan

You will get a list of something like this

File descriptor 3 left open
File descriptor 4 left open
/dev/dm-0 [ 9.67 GB]
/dev/sda1 [ 78.41 MB]
/dev/dm-1 [ 6.44 GB]
/dev/sda2 [ 115.52 GB]
/dev/dm-2 [ 2.00 GB]
/dev/sda3 [ 18.11 GB] LVM physical volume
/dev/sda5 [ 15.33 GB]

Make a note of /dev/dm-x, those are the devices which correspond to the LVM partitions. Also do note the sizes.

Next, type lvdisplay to show a detailed list of all logical volumes available.

lvdisplay |more

LV Name /dev/system/home
VG Name system
LV UUID 1QP9XM-vlKi-umNO-CXvV-TnZN-RCLk-e1FDIr
LV Write Access read/write
LV Status available
# open 1
LV Size 9.67 GB
Current LE 2475
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:0

— Logical volume —
LV Name /dev/system/root
VG Name system
LV UUID D1fKUJ-uU1C-jlVB-4imh-rrgy-FQu0-TC2Ssm
LV Write Access read/write
LV Status available
# open 1

LV Size 6.44 GB
Current LE 1649
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:1

— Logical volume —
LV Name /dev/system/swap
VG Name system
LV UUID w5LqIb-xvcr-Xsbk-y3wg-lT3i-LqdN-GFK8Mi
LV Write Access read/write
LV Status available
# open 0
LV Size 2.00 GB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:2

Now from the above set of data we can deduce that my /home partition, of size 9.67 GB is available as LV group /dev/system/home on /dev/dm-0

Now that we know where the partition is available, we can proceed with the mounting using the mount command, as

mount /dev/md-0 /home

And there you go, your LV partition is mounted!

Peter Westlake

You can get a list of volume names by running lvscan. The output will look like

/dev/VG1/LV1
/dev/VG1/LV2
/dev/VG2/LV3

i.e. with the volume group names in the middle and logical volumes at the end. See if any of them correspond to the information in Palimpset.

Also, compare to the list of disks already mounted (mount), and see which one isn't there. It might look a little different, e.g.:

$ mount
/dev/mapper/VG1-LV1 is mounted on /usr
/dev/mapper/VG1-LV2 is mounted on /home

You can see where the volume group and logical volume appear at the end.

Once you've found the right one, mount it in the usual way:

mount /dev/VG2/LV3 /mnt

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linux - LVM mount physical disk for backups