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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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volreattach(8)						      System Manager's Manual						    volreattach(8)

NAME
volreattach - Reattaches disk drives that have once again become accessible SYNOPSIS
/usr/sbin/volreattach [-rb] [accessname...] /usr/sbin/volreattach -c accessname OPTIONS
The volreattach utility has the following options: Calls the volrecover utility to attempt to recover stale plexes of any volumes on the failed disk. Performs the reattach operation in the background. Checks whether a reattach is possible. No operation is performed, but the name of the disk group and disk media name at which the disk can be reattached is displayed. DESCRIPTION
The volreattach utility attempts to reattach disks using the same disk group and media names they had before detachment. This operation may be necessary if a disk has a transient failure, or if some disk drivers are unloaded or unloadable when the Logical Storage Manager is started, causing disks to enter the failed state. If the problem is fixed, the volreattach command can be used to reattach the disks without plexes being flagged as stale, as long as the reattach happens before any volumes on the disk are started. The volreattach command is called from the voldiskadm menus as part of disk recovery. The volreattach utility tries to find a disk with a disk group and disk ID matching that of the disk(s) being reattached. If the matching disk is found, the reattach operation may still fail if the original cause (or some other cause) for the disk failure still exists. EXIT CODES
A zero exit status is returned if it is possible to perform a reattach. Otherwise, non-zero is returned. SEE ALSO
volintro(8), voldiskadm(8), volrecover(8) volreattach(8)
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