Logical Volume to physical disk mapping

Linux and Unix-Like Linux
1

When installing Linux, I choose some default setting to use all the disk space.

My server has a single internal 250Gb SCSI disk. By default the install appears to have created 3 logical volumes

lv_root, lv_home and lv_swap.

fdisk -l shows the following

lab3.nms:/dev>fdisk -l

Disk /dev/sde: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b3ade

   Device Boot      Start         End      Blocks   Id  System
/dev/sde1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sde2              64       30402   243685376   8e  Linux LVM

Disk /dev/mapper/vg_lab3-lv_root: 10.5 GB, 10485760000 bytes
255 heads, 63 sectors/track, 1274 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000


Disk /dev/mapper/vg_lab3-lv_swap: 4227 MB, 4227858432 bytes
255 heads, 63 sectors/track, 514 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000


Disk /dev/mapper/vg_lab3-lv_home: 52.4 GB, 52428800000 bytes
255 heads, 63 sectors/track, 6374 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

So the install appears to have created 2 partitions on /dev/sde i.e. /dev/sde1 and /dev/sde2

/dev/sde1 is the boot partition.

Q1. I am assuming that the logical volumes lv_root, lv_home and lv_swap are therefore using some of the space of /dev/sde2 - how do I prove / disprove that ?

Q2. During the linux install I decrease the size of lv_home to just over 50 Gb, leaving about 180 Gb unallocated. How do I see this unallocated space ?

any help appreciated,
Jim

2

Have a look at the vgdisplay command and see if that answers your queries.

Robin

3

pvs is good for showing space remaining in volumes across physical vols that are part of the logical vols.

When you create a volume group, it's from a pool of storage. In your case, the pool contains a single partition /dev/sde2 (at the time you posted anyhow). You'll practically never refer to /dev/sde2 again (there are cases, but generally only useful if you are creating volumes using whole drives rather than partitions).

Perhaps some good read here: NTLUG | Articles / LVM browse