Storage Management: Reference

I've been using LVM to work around the hassle of constantly changing hard disks, partitions, mounting shared data, etc.

Devices

List

List disk devices (not partitions), with sizes (in units of kibibytes — 1,024 bytes):
```
# sfdisk --show-size
```
Deprecated in favor of blockdev:
```
# blockdev --report
```
This shows sizes in bytes. And offsets of partitions into their disk device.
List all block devices (from sysfs/udev db), including loop devices, and their partitions — in tree view, with sizes, types, mount points:
```
$ lsblk
```
Table with just device names, major:minor, and sizes:
```
$ cat /proc/partitions
```
To list only physical, including USB attached, disks:
```
$ lsblk --scsi
```
This also shows hardware details: vendor, model, serial.
```
# lshw -short -class disk
```

Images

…

Partitions

Find

List briefly ("partprobe probes partition table for changes and informs OS". Foo?):

# partprobe -s
/dev/hda: msdos partitions 1 2 3 4 <5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25>
/dev/hdb: msdos partitions 1 2 <5 6 7 8 9 10 11 12 13 14 15 16 17 18>

UUID

List

List with geometry and sizes in MiB (-uM) or sectors (-uS):
```
# sfdisk --list -uM /dev/hda
```
Note MiB involves rounding. Use sectors for precision.

Analyze

Look for signatures:

# hexdump --canonical --length=9 /dev/loop2p1
00000000  eb 58 90 4d 53 44 4f 53  35                       |.X.MSDOS5|

Analyze content of (unmounted) partition — filtering through hexdump to see raw data, or through strings to look for text; looking in first 10 MiB:
```
# head --bytes=10m /dev/hda7 | hexdump --canonical | less
# head --bytes=10m /dev/sda3 | strings --all | less
```
If using less, also use head to limit amount of data read, because with large empty partitions these commands take forever to start displaying anything (I guess because less waits to fill the first page?):
```
# hexdump --canonical /dev/hda14 | less
# cat /dev/hda14 | strings --all | less
```
An empty (zeroed) partition produces this hexdump:
```
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00a00000
(END)
```
(Isn't the first cylinder (of every partition) ever used? Its first sector contains a partitions table, but the rest, which can be several megabytes long, is wasted?)

Create

Resize

Move

Test

Wipe

Overwrite with random data (generated by /dev/urandom):
```
# shred --verbose /dev/sda1
```

Delete

Encrypt

Volumes

Find

Scan for physical volumes (PV) (grep to filter device):

# pvscan
PV /dev/hda9 VG moved lvm2 [11.18 GB / 0 free]
PV /dev/hda10 VG moved lvm2 [3.73 GB / 0 free]
PV /dev/hda11 VG moved lvm2 [7.46 GB / 0 free]
PV /dev/hda12 VG moved lvm2 [11.18 GB / 4.06 GB free]
PV /dev/hda13 VG moved lvm2 [18.64 GB / 7.13 GB free]
Total: 5 [52.19 GB] / in use: 5 [52.19 GB] / in no VG: 0 [0 ]

Scan for logical volumes (LV):

# lvscan --verbose
   Finding all logical volumes
ACTIVE            '/dev/moved/sound' [1.00 GB] inherit
ACTIVE            '/dev/moved/star' [1.00 GB] inherit
ACTIVE            '/dev/moved/age' [9.00 GB] inherit
ACTIVE            '/dev/moved/knowledge' [8.00 GB] inherit
...

List

List volume groups (VG):

# vgs
VG #PV #LV #SN Attr VSize VFree
moved 6 20 0 wz--n 33.51G 3.51G

List LVs:

# lvs
LV        VG    Attr   LSize  Origin Snap%  Move Copy%
abstract  moved -wi-ao  1.00G
age       moved -wi-ao  9.00G
critic    moved -wi-ao  2.00G
cubism    moved -wi-ao  1.00G
fiction   moved -wi-ao  1.00G
knowledge moved -wi-ao  8.00G
mess      moved -wi-ao  1.00G
...

Displaying a LV's attriubtes:

# lvdisplay /dev/moved/abstract
--- Logical volume ---
LV Name                /dev/moved/abstract
VG Name                moved
LV UUID                Wd2DvY-UoSb-xsUY-Ywry-s7Cv-raXl-v5km3L
LV Write Access        read/write
LV Status              available
# open                 2
LV Size                1.00 GB
Current LE             256
Segments               1
Allocation             inherit
Read ahead sectors     0
Block device           254:13

The option --maps shows which physical volumes (partitions) and logical extents this volume occupies.

Create physical volumes (PV)

Formating a partition to make it a PV:

# pvcreate /dev/hda14
Physical volume "/dev/hda14" successfully created

Create volume groups (VG)

Adding a (formatted) PV to a VG:

# vgextend --verbose moved /dev/hda14
   Checking for volume group "moved"
   Archiving volume group "moved" metadata.
   Adding physical volume '/dev/hda14' to volume group 'moved'
   Volume group "moved" will be extended by 1 new physical volumes
   Creating volume group backup "/etc/lvm/backup/moved"
Volume group "moved" successfully extended

Create logical volumes (LV)

# lvcreate --size 80G --name progress heavy
  Logical volume "progress" created

Move

Moving a PV between VGs:

# vgreduce marf /dev/sdb9
# vgextend heavy /dev/sdb9
  Volume group "heavy" successfully extended

Resize

Removing LV from VG so can extend other LVs:

# lvs moved
  LV        VG    Attr   LSize  Origin Snap%  Move Log Copy%
  abstract  moved -wi-ao  5.46G
  age       moved -wi-ao 22.00G
...
# lvremove moved/mirror
Do you really want to remove active logical volume "mirror"? [y/n]: y
  Logical volume "mirror" successfully removed
# vgdisplay moved
  --- Volume group ---
  VG Name               moved
  System ID
  Format                lvm2
...
  Alloc PE / Size       37404 / 146.11 GB
  Free  PE / Size       256 / 1.00 GB

Extending LV and contained FS: first resize the LV, then the filesystem. With reiserfs, extending can be done while mounted, but for shrinking must unmount.

Resize (extend) LV (assumes VG has enough free space; specify final size with --size=9G or relative change — use extents, not size, for perfect sizing!):

# lvresize --verbose --size +1G /dev/moved/abstract
    Finding volume group moved
    Archiving volume group "moved" metadata.
  Extending logical volume abstract to 2.00 GB
    Creating volume group backup "/etc/lvm/backup/moved"
    Found volume group "moved"
    Found volume group "moved"
    Loading moved-abstract
  Logical volume abstract successfully resized

Resize (extend) FS. Given no parameters, resize_reiserfs stretches the FS to fill the partition (LV). For ext3: resize2fs. Note: do not add trailing slash.
```
# resize_reiserfs /dev/moved/abstract
resize_reiserfs 3.6.19 (2003 www.namesys.com)
resize_reiserfs: On-line resizing finished successfully.
```

Could have told LVM to --resizefs itself, but that fails:

# lvresize --verbose --size=4G --resizefs /dev/moved/surreal
   Finding volume group moved
   Executing: fsadm check /dev/moved/surreal (null)
fsadm: execlp failed: No such file or directory
fsadm failed: 2

Verify:

# df /vol/abstract/
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/moved-abstract
                     2097084   1013168   1083916  49% /vol/abstract

To extend an LV to fill the VG: check how many free extents (PE) remain, and resize:

# vgdisplay moved
  --- Volume group ---
  VG Name               moved
  System ID
  Format                lvm2
  Metadata Areas        6
  Metadata Sequence No  139
  VG Access             read/write
  VG Status             resizable
  MAX LV                255
  Cur LV                20
  Open LV               20
  Max PV                255
  Cur PV                6
  Act PV                6
  VG Size               55.91 GB
  PE Size               4.00 MB
  Total PE              14314
  Alloc PE / Size       13568 / 53.00 GB
  Free  PE / Size       746 / 2.91 GB
  VG UUID               vYRQuG-FKKQ-m937-Bmnr-ti0l-aWNi-4j1HcI

# lvresize --verbose --size +3G /dev/moved/noise
    Finding volume group moved
    Archiving volume group "moved" metadata.
  Extending logical volume noise to 15.00 GB
  Insufficient allocatable logical extents (3818) for logical volume noise: 3840 required

# lvresize --verbose --extents +746 /dev/moved/noise
    Finding volume group moved
    Archiving volume group "moved" metadata.
  Extending logical volume noise to 14.91 GB
    Creating volume group backup "/etc/lvm/backup/moved"
    Found volume group "moved"
    Found volume group "moved"
    Loading moved-noise
  Logical volume noise successfully resized

Followed by the usual resize_reiserfs (or resize2fs) and df.

Shrinking an LV and the file-system it contains: unmount, shrink the FS, then shrink the LV:

# resize_reiserfs -s 2G /dev/moved/age
resize_reiserfs 3.6.19 (2003 www.namesys.com)

Processing the tree:
0%....20%....40%....60%....80%....100% left 0, 8235 /sec

nodes processed (moved):
int        94 (1),
leaves     14490 (148),
unfm       298355 (143925),
total      312939 (144074).
check for used blocks in truncated region

ReiserFS report:
blocksize             4096
block count           524288 (2359296)
free blocks           203123 (2038075)
bitmap block count    16 (72)

Syncing..done
resize_reiserfs: Resizing finished successfully.

# lvresize --verbose --size 2G /dev/moved/age
   Finding volume group moved
WARNING: Reducing active logical volume to 2.00 GB
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce age? [y/n]: y
   Archiving volume group "moved" metadata.
Reducing logical volume age to 2.00 GB
   Creating volume group backup "/etc/lvm/backup/moved"
   Found volume group "moved"
   Found volume group "moved"
   Loading moved-age
Logical volume age successfully resized

# resize_reiserfs /dev/moved/age
resize_reiserfs 3.6.19 (2003 www.namesys.com)
/dev/moved/age already is of the needed size. Nothing to be done

But, failure?!

Can't shrink filesystem on-line.

resize_reiserfs: can't shrink fs; too many blocks already allocated
resize_reiserfs: Resizing failed.

Delete

Removing LV from VG:

# umount /vol/critic/
# lvremove moved/critic
Do you really want to remove active logical volume "critic"? [y/n]: n
  Logical volume "critic" not removed
# lvdisplay moved/critic
  --- Logical volume ---
  LV Name                /dev/moved/critic
  VG Name                moved
  LV UUID                mh6nr5-ZzuC-lG56-uhDB-5y5P-Bxq0-g1PmeX
  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     0
  Block device           254:13

# lvchange --available n moved/critic
# lvremove moved/critic
  Logical volume "critic" successfully removed

Wiping the PV signature from a partition:

# pvremove /dev/hdc18
Labels on physical volume "/dev/hdc18" successfully wiped

Storage Management: Reference

Devices

List

Images

Partitions

Find

UUID

List

Analyze

Create

Resize

Move

Test

Wipe

Delete

Encrypt

Volumes

Find

List

Create physical volumes (PV)

Create volume groups (VG)

Create logical volumes (LV)

Move

Resize

Delete

File systems

Analyze

Create

Un/mount

Space utilization

Wipe