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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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prtvtoc(1M)                                               System Administration Commands                                               prtvtoc(1M)

NAME
prtvtoc - report information about a disk geometry and partitioning SYNOPSIS
prtvtoc [-fhs] [-t vfstab] [-m mnttab] device DESCRIPTION
The prtvtoc command allows the contents of the label to be viewed. The command can be used only by the super-user. The device name can be the file name of a raw device in the form of /dev/rdsk/c?t?d?s2 or can be the file name of a block device in the form of /dev/dsk/c?t?d?s2. OPTIONS
The following options are supported: -f Report on the disk free space, including the starting block address of the free space, number of blocks, and unused parti- tions. -h Omit the headers from the normal output. -m mnttab Use mnttab as the list of mounted filesystems, in place of /etc/mnttab. -s Omit all headers but the column header from the normal output. -t vfstab Use vfstab as the list of filesystem defaults, in place of /etc/vfstab. EXAMPLES
Example 1: Using the prtvtoc Command The following example uses the prtvtoc command on a 424-megabyte hard disk: example# prtvtoc /dev/rdsk/c0t3d0s2 * /dev/rdsk/c0t3d0s2 partition map * * Dimension: * 512 bytes/sector * 80 sectors/track * 9 tracks/cylinder * 720 sectors/cylinder * 2500 cylinders * 1151 accessible cylinders * * Flags: * 1: unmountable * 10: read-only * * First Sector Last * Partition Tag Flags Sector Count Sector Mount Directory 0 2 00 0 76320 76319 / 1 3 01 76320 132480 208799 2 5 00 0 828720 828719 5 6 00 208800 131760 340559 /opt 6 4 00 340560 447120 787679 /usr 7 8 00 787680 41040 828719 /export/home example# The data in the Tag column above indicates the type of partition, as follows: Name Number UNASSIGNED 0x00 BOOT 0x01 ROOT 0x02 SWAP 0x03 USR 0x04 BACKUP 0x05 STAND 0x06 VAR 0x07 HOME 0x08 ALTSCTR 0x09 CACHE 0x0a RESERVED 0x0b The data in the Flags column above indicates how the partition is to be mounted, as follows: Name Number MOUNTABLE, READ AND WRITE 0x00 NOT MOUNTABLE 0x01 MOUNTABLE, READ ONLY 0x10 Example 2: Using the prtvtoc Command with the -f Option The following example uses the prtvtoc command with the -f option on a 424-megabyte hard disk: example# prtvtoc -f /dev/rdsk/c0t3d0s2 FREE_START=0 FREE_SIZE=0 FREE_COUNT=0 FREE_PART=34 Example 3: Using the prtvtoc Command on a Disk Over One Terabyte The following example uses uses the prtvtoc command on a disk over one terabyte:. example# prtvtoc /dev/rdsk/c1t1d0s2 * /dev/rdsk/c1t1d0s2 partition map * * Dimensions: * 512 bytes/sector * 3187630080 sectors * 3187630013 accessible sectors * * Flags: * 1: unmountable * 10: read-only * * First Sector Last * Partition Tag Flags Sector Count Sector Mount Directory 0 2 00 34 262144 262177 1 3 01 262178 262144 524321 6 4 00 524322 3187089340 3187613661 8 11 00 3187613662 16384 318763004 ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
devinfo(1M), fmthard(1M), format(1M), mount(1M), attributes(5) WARNINGS
The mount command does not check the "not mountable" bit. SunOS 5.10 25 Jul 2002 prtvtoc(1M)
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