8.2. Creating thinly-provisioned logical volumes

Procédure

1. Create a thin pool:

   # lvcreate -L 100M -T vg001/mythinpool
     Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
     Logical volume "mythinpool" created.

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   Note that since you are creating a pool of physical space, you must specify the size of the pool. The -T option of the lvcreate command does not take an argument; it determines what type of device is to be created from the other options that are added with the command. You can also create thin pool using additional parameters as shown in the following examples:

   • You can also create a thin pool using the --thinpool parameter of the lvcreate command. Unlike the -T option, the --thinpool parameter requires that you specify the name of the thin pool logical volume you are creating. The following example uses the --thinpool parameter to create a thin pool named mythinpool in the volume group vg001 that is 100M in size:

     # lvcreate -L 100M --thinpool mythinpool vg001
       Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
       Logical volume "mythinpool" created.

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   • As striping is supported for pool creation, you can use the -i and -I options to create stripes. The following command creates a 100M thin pool named as thinpool in volume group vg001 with two 64 kB stripes and a chunk size of 256 kB. It also creates a 1T thin volume named vg001/thinvolume.

     Note

     Ensure that there are two physical volumes with sufficient free space in the volume group or you cannot create the thin pool.

     # lvcreate -i 2 -I 64 -c 256 -L 100M -T vg001/thinpool -V 1T --name thinvolume

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2. Create a thin volume:

   # lvcreate -V 1G -T vg001/mythinpool -n thinvolume
     WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin pool vg001/mythinpool (100.00 MiB).
     WARNING: You have not turned on protection against thin pools running out of space.
     WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
     Logical volume "thinvolume" created.

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   In this case, you are specifying virtual size for the volume that is greater than the pool that contains it. You can also create thin volumes using additional parameters as shown in the following examples:

   • To create both a thin volume and a thin pool, use the -T option of the lvcreate command and specify both the size and virtual size argument:

     # lvcreate -L 100M -T vg001/mythinpool -V 1G -n thinvolume
       Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
       WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin pool vg001/mythinpool (100.00 MiB).
       WARNING: You have not turned on protection against thin pools running out of space.
       WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
       Logical volume "thinvolume" created.

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   • To use the remaining free space to create a thin volume and thin pool, use the 100%FREE option:

     # lvcreate -V 1G -l 100%FREE -T vg001/mythinpool -n thinvolume
     Thin pool volume with chunk size 64.00 KiB can address at most <15.88 TiB of data.
       Logical volume "thinvolume" created.

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   • To convert an existing logical volume to a thin pool volume, use the --thinpool parameter of the lvconvert command. You must also use the --poolmetadata parameter in conjunction with the --thinpool parameter to convert an existing logical volume to a thin pool volume’s metadata volume.

     The following example converts the existing logical volume lv1 in volume group vg001 to a thin pool volume and converts the existing logical volume lv2 in volume group vg001 to the metadata volume for that thin pool volume:

     # lvconvert --thinpool vg001/lv1 --poolmetadata vg001/lv2
       Converted vg001/lv1 to thin pool.

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     Note

     Converting a logical volume to a thin pool volume or a thin pool metadata volume destroys the content of the logical volume, as lvconvert does not preserve the content of the devices but instead overwrites the content.

   • By default, the lvcreate command approximately sets the size of the thin pool metadata logical volume by using the following formula:

     Pool_LV_size / Pool_LV_chunk_size * 64

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     If you have large numbers of snapshots or if you have have small chunk sizes for your thin pool and therefore expect significant growth of the size of the thin pool at a later time, you may need to increase the default value of the thin pool’s metadata volume using the --poolmetadatasize parameter of the lvcreate command. The supported value for the thin pool’s metadata logical volume is in the range between 2MiB and 16GiB.

     The following example illustrates how to increase the default value of the thin pools’ metadata volume:

     # lvcreate -V 1G -l 100%FREE -T vg001/mythinpool --poolmetadatasize 16M -n thinvolume
     Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
        Logical volume "thinvolume" created.

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3. View the created thin pool and thin volume:

   # lvs -a -o +devices
     LV                 VG    Attr       LSize   Pool       Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices
     [lvol0_pmspare]    vg001 ewi-------   4.00m                                                           /dev/sda(0)
     mythinpool         vg001 twi-aotz-- 100.00m                   0.00   10.94                            mythinpool_tdata(0)
     [mythinpool_tdata] vg001 Twi-ao---- 100.00m                                                           /dev/sda(1)
     [mythinpool_tmeta] vg001 ewi-ao----   4.00m                                                           /dev/sda(26)
     thinvolume         vg001 Vwi-a-tz--   1.00g mythinpool        0.00

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4. Optional: Extend the size of a thin pool with the lvextend command. You cannot, however, reduce the size of a thin pool.

   Note

   This command fails if you use -l 100%FREE argument while creating a thin pool and thin volume.

   The following command resizes an existing thin pool that is 100M in size by extending it another 100M:

   # lvextend -L+100M vg001/mythinpool
     Size of logical volume vg001/mythinpool_tdata changed from 100.00 MiB (25 extents) to 200.00 MiB (50 extents).
     WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin pool vg001/mythinpool (200.00 MiB).
     WARNING: You have not turned on protection against thin pools running out of space.
     WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
   
     Logical volume vg001/mythinpool successfully resized

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   # lvs -a -o +devices
     LV                 VG    Attr       LSize   Pool       Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices
     [lvol0_pmspare]    vg001 ewi-------   4.00m                                                           /dev/sda(0)
     mythinpool         vg001 twi-aotz-- 200.00m                   0.00   10.94                            mythinpool_tdata(0)
     [mythinpool_tdata] vg001 Twi-ao---- 200.00m                                                           /dev/sda(1)
     [mythinpool_tdata] vg001 Twi-ao---- 200.00m                                                           /dev/sda(27)
     [mythinpool_tmeta] vg001 ewi-ao----   4.00m                                                           /dev/sda(26)
     thinvolume         vg001 Vwi-a-tz--   1.00g mythinpool        0.00

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5. Optional: To rename the thin pool and thin volume, use the following command:

   # lvrename vg001/mythinpool vg001/mythinpool1
     Renamed "mythinpool" to "mythinpool1" in volume group "vg001"
   
   # lvrename vg001/thinvolume vg001/thinvolume1
     Renamed "thinvolume" to "thinvolume1" in volume group "vg001"

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   View the thin pool and thin volume after renaming:

   # lvs
     LV          VG       Attr     LSize   Pool       Origin Data%  Move Log Copy%  Convert
   mythinpool1 vg001   twi-a-tz 100.00m                     0.00
   thinvolume1 vg001   Vwi-a-tz   1.00g mythinpool1         0.00

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6. Optional: To remove the thin pool, use the following command:

   # lvremove -f vg001/mythinpool1
     Logical volume "thinvolume1" successfully removed.
     Logical volume "mythinpool1" successfully removed.

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