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Operating Systems Linux Logical Volume to physical disk mapping Post 302883003 by jimthompson on Friday 10th of January 2014 11:03:00 AM
Old 01-10-2014
Logical Volume to physical disk mapping

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

Code:
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

Last edited by bartus11; 01-10-2014 at 12:18 PM.. Reason: Please use code tags.
 

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DD(1)							      General Commands Manual							     DD(1)

NAME
dd - disk dumper SYNOPSIS
dd [option = value] ... EXAMPLES
dd if=/dev/fd0 of=/dev/fd1 # Copy disk 0 to disk 1 dd if=x of=y bs=1w skip=4 # Copy x to y, skipping 4 words dd if=x of=y count=3 # Copy three 512-byte blocks DESCRIPTION
This command is intended for copying partial files. The block size, skip count, and number of blocks to copy can be specified. The options are: if = file - Input file (default is stdin) of = file - Output file (default is standard output) ibs = n - Input block size (default 512 bytes) obs = n - Output block size (default is 512 bytes) bs = n - Block size; sets ibs and obs (default is 512 bytes) skip = n - Skip n input blocks before reading seek = n - Skip n output blocks before writing count = n - Copy only n input blocks conv = lcase - Convert upper case letters to lower case conv = ucase - Convert lower case letters to upper case conv = swab - Swap every pair of bytes conv = noerror- Ignore errors and just keep going conv = silent- Suppress statistics (Minix specific flag) Where sizes are expected, they are in bytes. However, the letters w, b, or k may be appended to the number to indicate words (2 bytes), blocks (512 bytes), or K (1024 bytes), respectively. When dd is finished, it reports the number of full and partial blocks read and writ- ten. SEE ALSO
vol(1). DD(1)
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