15.2. Common SSM Tasks

The following sections will go through basic use cases covering how to install SSM then display information about all detected devices, pools, and volumes. Next, a pool will be created with two volumes and an XFS file system. The file system will then be checked for consistency, then a volume will be increased in size. Then a snapshot will be created. Finally one of the volumes will be removed.

15.2.1. Installing SSM

To install SSM use the following command:
# yum install system-storage-manager
There are several back ends that are enabled only if the supporting packages are installed:
  • The LVM back end requires the lvm2 package.
  • The Btrfs back end requires the btrfs-progs package.
  • The Crypt back end requires the device-mapper and cryptsetup packages.

15.2.2. Displaying Information about All Detected Devices

Displaying information about all detected devices, pools, volumes, and snapshots is done with the list command. Running the ssm list with no options will display the following output:
~]# ssm list
----------------------------------------------------------
Device        Free      Used      Total  Pool  Mount point
----------------------------------------------------------
/dev/sda                        2.00 GB        PARTITIONED
/dev/sda1                      47.83 MB        /test
/dev/vda                       15.00 GB        PARTITIONED
/dev/vda1                     500.00 MB        /boot
/dev/vda2  0.00 KB  14.51 GB   14.51 GB  rhel
----------------------------------------------------------
------------------------------------------------
Pool  Type  Devices     Free      Used     Total
------------------------------------------------
rhel  lvm   1        0.00 KB  14.51 GB  14.51 GB
------------------------------------------------
---------------------------------------------------------------------------------
Volume          Pool  Volume size  FS     FS size       Free  Type    Mount point
---------------------------------------------------------------------------------
/dev/rhel/root  rhel     13.53 GB  xfs   13.52 GB    9.64 GB  linear  /
/dev/rhel/swap  rhel   1000.00 MB                             linear
/dev/sda1                47.83 MB  xfs   44.50 MB   44.41 MB  part    /test
/dev/vda1               500.00 MB  xfs  496.67 MB  403.56 MB  part    /boot
---------------------------------------------------------------------------------
This display can be further narrowed down by using arguments to specify what should be displayed. The list of available options can be found with the ssm list --help command.

Note

Depending on the argument given, SSM may not display everything.
  • Running the devices or dev argument will omit some devices. CDRoms and DM/MD devices, for example, are intentionally hidden as they are listed as volumes.
  • Some back ends do not support snapshots and cannot distinguish between a snapshot and a regular volume. Running the snapshot argument on one of these back ends will cause SSM to attempt to recognize the volume name in order to identify a snapshot. If the SSM regular expression does not match the snapshot pattern then the snapshot will not be recognized.
  • With the exception of the main Btrfs volume (the file system itself), any unmounted Btrfs volumes will not be shown.

15.2.3. Creating a New Pool, Logical Volume, and File System

In this section, a new pool will be created with a default name. It will have the devices /dev/vdb and /dev/vdc, a logical volume of 1G, and an XFS file system.
The command to create this scenario is ssm create --fs xfs -s 1G /dev/vdb /dev/vdc. The following options are used:
  • The --fs option specifies the required file system type. Current supported file system types are:
    • ext3
    • ext4
    • xfs
    • btrfs
  • The -s specifies the size of the logical volume. The following suffixes are supported to define units:
    • K or k for kilobytes
    • M or m for megabytes
    • G or g for gigabytes
    • T or t for terabytes
    • P or p for petabytes
    • E or e for exabytes
  • The two listed devices, /dev/vdb and /dev/vdc, are the two devices I wish to create.
~]# ssm create --fs xfs -s 1G /dev/vdb /dev/vdc
  Physical volume "/dev/vdb" successfully created
  Physical volume "/dev/vdc" successfully created
  Volume group "lvm_pool" successfully created
  Logical volume "lvol001" created
There are two other options for the ssm command that may be useful. The first is the -p pool command. This specifies the pool the volume is to be created on. If it does not yet exist, then SSM will create it. This was omitted in the above example which caused SSM to use the default name lvm_pool. However, to use a specific name to fit in with any existing naming conventions, the -p option should be used.
The second useful option is the -n name command. This names the newly created logical volume. As with the -p, this is needed in order to use a specific name to fit in with any existing naming conventions.
An example of these two options being used follows:
~]# ssm create --fs xfs -p new_pool -n XFS_Volume /dev/vdd
  Volume group "new_pool" successfully created
  Logical volume "XFS_Volume" created
SSM has now created two physical volumes, a pool, and a logical volume with the ease of only one command.

15.2.4. Checking a File System's Consistency

The ssm check command checks the file system consistency on the volume. It is possible to specify multiple volumes to check. If there is no file system on the volume, then the volume will be skipped.
To check all devices in the volume lvol001, run the command ssm check /dev/lvm_pool/lvol001.
~]# ssm check /dev/lvm_pool/lvol001
Checking xfs file system on '/dev/mapper/lvm_pool-lvol001'.
Phase 1 - find and verify superblock...
Phase 2 - using internal log
        - scan filesystem freespace and inode maps...
        - found root inode chunk
Phase 3 - for each AG...
        - scan (but don't clear) agi unlinked lists...
        - process known inodes and perform inode discovery...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
        - agno = 4
        - agno = 5
        - agno = 6
        - process newly discovered inodes...
Phase 4 - check for duplicate blocks...
        - setting up duplicate extent list...
        - check for inodes claiming duplicate blocks...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
        - agno = 4
        - agno = 5
        - agno = 6
No modify flag set, skipping phase 5
Phase 6 - check inode connectivity...
        - traversing filesystem ...
        - traversal finished ...
        - moving disconnected inodes to lost+found ...
Phase 7 - verify link counts...
No modify flag set, skipping filesystem flush and exiting.

15.2.5. Increasing a Volume's Size

The ssm resize command changes the size of the specified volume and file system. If there is no file system then only the volume itself will be resized.
For this example, we currently have one logical volume on /dev/vdb that is 900MB called lvol001.
~]# ssm list
-----------------------------------------------------------------
Device          Free       Used      Total  Pool      Mount point
-----------------------------------------------------------------
/dev/vda                          15.00 GB            PARTITIONED
/dev/vda1                        500.00 MB            /boot
/dev/vda2    0.00 KB   14.51 GB   14.51 GB  rhel
/dev/vdb   120.00 MB  900.00 MB    1.00 GB  lvm_pool
/dev/vdc                           1.00 GB
-----------------------------------------------------------------
---------------------------------------------------------
Pool      Type  Devices       Free       Used       Total
---------------------------------------------------------
lvm_pool  lvm   1        120.00 MB  900.00 MB  1020.00 MB
rhel      lvm   1          0.00 KB   14.51 GB    14.51 GB
---------------------------------------------------------
--------------------------------------------------------------------------------------------
Volume                 Pool      Volume size  FS     FS size       Free  Type    Mount point
--------------------------------------------------------------------------------------------
/dev/rhel/root         rhel         13.53 GB  xfs   13.52 GB    9.64 GB  linear  /
/dev/rhel/swap         rhel       1000.00 MB                             linear
/dev/lvm_pool/lvol001  lvm_pool    900.00 MB  xfs  896.67 MB  896.54 MB  linear
/dev/vda1                          500.00 MB  xfs  496.67 MB  403.56 MB  part    /boot
--------------------------------------------------------------------------------------------
The logical volume needs to be increased by another 500MB. To do so we will need to add an extra device to the pool:
~]# ssm resize -s +500M /dev/lvm_pool/lvol001 /dev/vdc
  Physical volume "/dev/vdc" successfully created
  Volume group "lvm_pool" successfully extended
Phase 1 - find and verify superblock...
Phase 2 - using internal log
        - scan filesystem freespace and inode maps...
        - found root inode chunk
Phase 3 - for each AG...
        - scan (but don't clear) agi unlinked lists...
        - process known inodes and perform inode discovery...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
        - process newly discovered inodes...
Phase 4 - check for duplicate blocks...
        - setting up duplicate extent list...
        - check for inodes claiming duplicate blocks...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
No modify flag set, skipping phase 5
Phase 6 - check inode connectivity...
        - traversing filesystem ...
        - traversal finished ...
        - moving disconnected inodes to lost+found ...
Phase 7 - verify link counts...
No modify flag set, skipping filesystem flush and exiting.
  Extending logical volume lvol001 to 1.37 GiB
  Logical volume lvol001 successfully resized
meta-data=/dev/mapper/lvm_pool-lvol001 isize=256    agcount=4, agsize=57600 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=0
data     =                       bsize=4096   blocks=230400, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
log      =internal               bsize=4096   blocks=853, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 230400 to 358400

SSM runs a check on the device and then extends the volume by the specified amount. This can be verified with the ssm list command.
~]# ssm list
------------------------------------------------------------------
Device          Free        Used      Total  Pool      Mount point
------------------------------------------------------------------
/dev/vda                           15.00 GB            PARTITIONED
/dev/vda1                         500.00 MB            /boot
/dev/vda2    0.00 KB    14.51 GB   14.51 GB  rhel
/dev/vdb     0.00 KB  1020.00 MB    1.00 GB  lvm_pool
/dev/vdc   640.00 MB   380.00 MB    1.00 GB  lvm_pool
------------------------------------------------------------------
------------------------------------------------------
Pool      Type  Devices       Free      Used     Total
------------------------------------------------------
lvm_pool  lvm   2        640.00 MB   1.37 GB   1.99 GB
rhel      lvm   1          0.00 KB  14.51 GB  14.51 GB
------------------------------------------------------
----------------------------------------------------------------------------------------------
Volume                 Pool      Volume size  FS      FS size        Free  Type    Mount point
----------------------------------------------------------------------------------------------
/dev/rhel/root         rhel         13.53 GB  xfs    13.52 GB     9.64 GB  linear  /
/dev/rhel/swap         rhel       1000.00 MB                               linear
/dev/lvm_pool/lvol001  lvm_pool      1.37 GB  xfs     1.36 GB     1.36 GB  linear
/dev/vda1                          500.00 MB  xfs   496.67 MB   403.56 MB  part    /boot
----------------------------------------------------------------------------------------------

Note

It is only possible to decrease an LVM volume's size; it is not supported with other volume types. This is done by using a - instead of a +. For example, to decrease the size of an LVM volume by 50M the command would be:
~]# ssm resize -s-50M /dev/lvm_pool/lvol002
  Rounding size to boundary between physical extents: 972.00 MiB
  WARNING: Reducing active logical volume to 972.00 MiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce lvol002? [y/n]: y
  Reducing logical volume lvol002 to 972.00 MiB
  Logical volume lvol002 successfully resized
Without either the + or -, the value is taken as absolute.

15.2.6. Snapshot

To take a snapshot of an existing volume, use the ssm snapshot command.

Note

This operation will fail if the back end the volume belongs to does not support snapshotting.
To create a snapshot of the lvol001, use the following command:
~]# ssm snapshot /dev/lvm_pool/lvol001
  Logical volume "snap20150519T130900" created
To verify this, use the ssm list, and note the extra snapshot section.
~]# ssm list
----------------------------------------------------------------
Device        Free        Used      Total  Pool      Mount point
----------------------------------------------------------------
/dev/vda                         15.00 GB            PARTITIONED
/dev/vda1                       500.00 MB            /boot
/dev/vda2  0.00 KB    14.51 GB   14.51 GB  rhel
/dev/vdb   0.00 KB  1020.00 MB    1.00 GB  lvm_pool
/dev/vdc                          1.00 GB
----------------------------------------------------------------
--------------------------------------------------------
Pool      Type  Devices     Free        Used       Total
--------------------------------------------------------
lvm_pool  lvm   1        0.00 KB  1020.00 MB  1020.00 MB
rhel      lvm   1        0.00 KB    14.51 GB    14.51 GB
--------------------------------------------------------
----------------------------------------------------------------------------------------------
Volume                 Pool      Volume size  FS      FS size        Free  Type    Mount point
----------------------------------------------------------------------------------------------
/dev/rhel/root         rhel         13.53 GB  xfs    13.52 GB     9.64 GB  linear  /
/dev/rhel/swap         rhel       1000.00 MB                               linear
/dev/lvm_pool/lvol001  lvm_pool    900.00 MB  xfs   896.67 MB   896.54 MB  linear
/dev/vda1                          500.00 MB  xfs   496.67 MB   403.56 MB  part    /boot
----------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------
Snapshot                           Origin   Pool      Volume size     Size  Type
----------------------------------------------------------------------------------
/dev/lvm_pool/snap20150519T130900  lvol001  lvm_pool    120.00 MB  0.00 KB  linear
----------------------------------------------------------------------------------

15.2.7. Removing an Item

The ssm remove is used to remove an item, either a device, pool, or volume.

Note

If a device is being used by a pool when removed, it will fail. This can be forced using the -f argument.
If the volume is mounted when removed, it will fail. Unlike the device, it cannot be forced with the -f argument.
To remove the lvm_pool and everything within it use the following command:
~]# ssm remove lvm_pool
Do you really want to remove volume group "lvm_pool" containing 2 logical volumes? [y/n]: y
Do you really want to remove active logical volume snap20150519T130900? [y/n]: y
  Logical volume "snap20150519T130900" successfully removed
Do you really want to remove active logical volume lvol001? [y/n]: y
  Logical volume "lvol001" successfully removed
  Volume group "lvm_pool" successfully removed