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Chapter 7. Customizing the LVM report

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LVM provides a wide range of configuration and command line options to produce customized reports and to filter the report’s output. You can sort the output, specify units, use selection criteria, and update the lvm.conf file to customize the LVM report.

7.1. Controlling format of the LVM display

Whether you use pvs, lvs, or vgs, these commands determine the default set of fields displayed and the sort order. You can control the output of these commands by executing the following commands.

Procedure

  • Change the default fields in the LVM display using the -o option: 

    # pvs -o pv_name,pv_size,pv_free
  PV         PSize  PFree
  /dev/vdb1  17.14G 17.14G
  /dev/vdb2  17.14G 17.09G
  /dev/vdb3  17.14G 17.14G

  • Sort LVM display by using the -O option: 

    # pvs -o pv_name,pv_size,pv_free -O pv_free
  PV         PSize  PFree
  /dev/vdb2 17.14G 17.09G
  /dev/vdb1  17.14G 17.14G
  /dev/vdb3  17.14G 17.14G

  • Display a reverse sort by using the -O argument along with the - character: 

    # pvs -o pv_name,pv_size,pv_free -O -pv_free
  PV         PSize  PFree
  /dev/vdb1  17.14G 17.14G
  /dev/vdb3  17.14G 17.14G
  /dev/vdb2  17.14G 17.09G

Additional resources

7.2. Specifying the units for an LVM report display

You can view the size of the LVM devices in base 2 or base 10 units by specifying the --units argument of the report command.

Base 2 units

The default units are displayed in powers of 2, which is multiples of 1024. You can specify it using human-readable (r) with < and > rounding indicator, bytes (b), sectors (s), kilobytes (k), megabytes (m), gigabytes (g), terabytes (t), petabytes (p), exabytes (e), and human-readable (h).

The default display is r, when --units is not specified. You can override the default by setting the units parameter in the global section of the /etc/lvm/lvm.conf file.

Base 10 units
You can specify the units to be displayed in multiples of 1000 by capitalizing the unit specification (R, B, S, K, M, G, T, P, E, H).

Procedure

  • Specify the units for the LVM for base 2 gigabytes units: 

    # pvs --units g /dev/vdb
  PV        VG    Fmt  Attr PSize   PFree
  /dev/vdb  myvg  lvm2 a--  931.00g 930.00g

# vgs --units g myvg
  VG   #PV #LV #SN Attr VSize   VFree
  myvg   1   1   0 wz-n 931.00g 931.00g

# lvs --units g myvg
  LV    VG   Attr     LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  mylv myvg  wi-a---- 1.OOg

  • Indicate the actual size of LVM by using the r option with the < or > prefix in the output: 

    # vgs --units g myvg
  VG   #PV #LV #SN Attr VSize   VFree
  myvg   1   1   0 wz-n 931.00g 930.00g

# vgs --units r myvg
  VG   #PV #LV #SN Attr VSize    VFree
  myvg   1   1   0 wz-n <931.00g <930.00

# vgs myvg
  VG   #PV #LV #SN Attr VSize    VFree
  myvg   1   1   0 wz-n <931.00g <930.00g

    The r unit works similarly to h (human-readable), but in addition, the reported value gets a prefix of < or > to indicate that the actual size is slightly more or less than the displayed size. LVM rounds the decimal value, causing non-exact sizes to be reported.

    It also shows how --units g or other --units do not always display exactly correct sizes. It also shows the primary purpose of r, which is the < to indicate that the displayed size is not exact. In this example, the value is not exact because the VG size is not an exact multiple of gigabytes, and .01 is also not an exact representation of the fraction.

  • Specify the units for the LVM for base 10 gigabytes units: 

    # pvs --units G /dev/vdb
  PV        VG   Fmt  Attr  PSize   PFree
  /dev/vdb  myvg lvm2 a--   999.65G 998.58G

# vgs --units G myvg
  VG   #PV #LV #SN Attr VSize   VFree
  myvg   1   1   0 wz-n 999.65G 998.58G

# lvs --units G myvg
  LV    VG   Attr     LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  mylv myvg wi-a---- 1.07G

  • Specify sectors (s), defined as 512 bytes, or custom units. The following example displays the output of the pvs command as several sectors: 

    # pvs --units s
  PV         VG     Fmt  Attr PSize       PFree
  /dev/vdb   myvg   lvm2 a--  1952440320S 1950343168S

  • Specify megabytes (m). The following example displays the output of the pvs command in units of 4 MB: 

    # pvs --units 4m
  PV         VG     Fmt  Attr PSize      PFree
  /dev/vdb   myvg   lvm2 a--  238335.00U 238079.00U

7.3. Customizing the LVM configuration file

By editing the lvm.conf file, you can customize the LVM according to your specific storage and system requirements. For example, you can use lvm.conf to modify filter settings, configure volume group auto activation, manage thin pool, or automatically extend a snapshot.

Procedure:

  1. Display the default lvm.conf file: 

    # lvmconfig --typeconfig default --withcomments

    By default, the lvm.conf file contains only comments to display possible settings.

  2. Customize the lvm.conf file according to your requirements by uncommenting the setting in lvm.conf. The following setting focuses on changing the default display of certain commands:

    • In the lvm.conf file, adjust the lvs_cols parameter to only print the specified fields: 

      {
  ...
  lvs_cols="lv_name,vg_name,lv_attr"
  ...
}

      Use this option instead of the lvs -o lv_name,vg_name,lv_attr command to avoid unnecessary frequent use of the -o option.

    • In the lvm.conf file, use the compact_output=1 setting to avoid printing empty fields for the pvs, vgs, and lvs commands: 

      {
  ...
  compact_output = 1
  ...
}

  3. View the default values after modifying the lvm.conf file: 

    # lvmconfig --typeconfig diff

Additional resources

  • lvm.conf(5) man page

7.4. Defining LVM selection criteria

Selection criteria are a set of statements in the form of <field> <operator> <value>, which use comparison operators to define values for specific fields. Objects that match the selection criteria are then processed or displayed. Statements are combined by logical and grouping operators. To define selection criteria use the -S or --select option followed by one or multiple statements.

Some LVM commands support the -S option to select which objects to process based on certain attributes. These objects can be physical volumes (PVs), volume groups (VGs), or logical volumes (LVs).

The -S option works by describing the objects to process, rather than naming each object. This is helpful when processing many objects and it would be difficult to find and name each object separately or when searching objects that have a complex set of characteristics. The select option can also be used as a shortcut to avoid typing many names.

Use the lvs -S help command to see full sets of fields and possible operators. Replace lvs with any reporting or processing command to see the details of that command.

Use selection criteria with LVM reporting and processing commands to only display or process the objects that satisfy chosen criteria:

  • Reporting commands include pvs, vgs, lvs, pvdisplay, vgdisplay, lvdisplay, and dmsetup info -c.
  • Processing commands include pvchange, vgchange, lvchange, vgimport, vgexport, vgremove, and lvremove.

Procedure

  • Examples of selection criteria using the pvs command: 

    # pvs
  PV           VG   Fmt  Attr PSize    PFree
  /dev/nvme2n1       lvm2 ---     1.00g   1.00g
  /dev/vdb1     myvg lvm2 a--  1020.00m 396.00m
  /dev/vdb2     myvg lvm2 a--  1020.00m 896.00m
    # pvs -S name=~nvme
  PV           Fmt  Attr PSize PFree
  /dev/nvme2n1 lvm2 ---  1.00g 1.00g
    # pvs -S vg_name=myvg
  PV         VG   Fmt  Attr PSize    PFree
  /dev/vdb1   myvg lvm2 a--  1020.00m 396.00m
  /dev/vdb2   myvg lvm2 a--  1020.00m 896.00m

  • Examples of selection criteria using the lvs commands: 

    # lvs
  LV    VG   Attr       LSize   Cpy%Sync
  mylv  myvg -wi-a----- 200.00m
  lvol0 myvg -wi-a----- 100.00m
  lvol1 myvg -wi-a----- 100.00m
  lvol2 myvg -wi------- 100.00m
  rr    myvg rwi-a-r--- 120.00m 100.00
    # lvs -S 'size > 100m && size < 200m'
  LV   VG   Attr       LSize   Cpy%Sync
  rr   myvg rwi-a-r--- 120.00m 100.00
    # lvs -S name=~lvol[02]
  LV    VG   Attr       LSize
  lvol0 myvg -wi-a----- 100.00m
  lvol2 myvg -wi------- 100.00m
    # lvs -S segtype=raid1
  LV   VG   Attr       LSize   Cpy%Sync
  rr   myvg rwi-a-r--- 120.00m 100.00

  • More advanced examples: 

    # lvchange --addtag mytag -S active=1
  Logical volume myvg/mylv changed.
  Logical volume myvg/lvol0 changed.
  Logical volume myvg/lvol1 changed.
  Logical volume myvg/rr changed.
    # lvs -a -o lv_name,vg_name,attr,size,pool_lv,origin,role -S 'name!~_pmspare'
  LV         VG      Attr       LSize Pool Origin Role
  thin1      example Vwi-a-tz-- 2.00g tp          public,origin,thinorigin
  thin1s     example Vwi---tz-- 2.00g tp   thin1  public,snapshot,thinsnapshot
  thin2      example Vwi-a-tz-- 3.00g tp          public
  tp         example twi-aotz-- 1.00g             private
  [tp_tdata] example Twi-ao---- 1.00g             private,thin,pool,data
  [tp_tmeta] example ewi-ao---- 4.00m             private,thin,pool,metadata
    # lvchange --setactivationskip n -S 'role=thinsnapshot && origin=thin1'
  Logical volume myvg/thin1s changed.
    # lvs -a -S 'name=~_tmeta && role=metadata && size <= 4m'
  LV         VG      Attr       LSize
  [tp_tmeta] myvg   ewi-ao---- 4.00m

Additional resources

  • lvmreport(7) man page
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