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+====== Use External Disk for Caching ======
+An external disk, such as an SSD or NVME can be used to cache an existing LVM logical volume. In combination with qemu/kvm virtualization, this can speed up virtual machines considerably as well as reduce pressure on mechanical storage.
+Assuming that a physical volume along with a volume group and a few logical volumes exist that have to be cached, the following commands can be used to attach an SSD or NVME drive and enable caching for the various logical volumes.
+The physical disk layout is the following (by issuing the ''pvs''):
+<code>
+  PV           VG  Fmt  Attr PSize    PFree
+  /dev/sda2    vms lvm2 a--   800.00g <410.20g
+</code>
+revealing a slow drive (origin drive) ''/dev/sda2''.
+Now, an NVME drive is used to create a new LVM physical disk:
+<code bash>
+pvcreate /dev/nvme0n1
+</code>
+resulting in the following configuration:
+<code>
+  PV           VG  Fmt  Attr PSize    PFree
+  /dev/nvme0n1 vms lvm2 a--  <476.94g <476.94g
+  /dev/sda2    vms lvm2 a--   800.00g <410.20g
+</code>
+Note that the entire NVME drive has been used instead of a partitioning the NVME drive (''/dev/nvme0n1'' instead of ''/dev/nvme0n1p1'') but that is a matter of choice and a partition can be created instead to be used for caching.
+Next, it is assumed that a volume group (''vms'') already exists (command issued: ''vgs''):
+<code>
+  VG  #PV #LV #SN Attr   VSize VFree
+  vms   2  11   0 wz--n- 1.15t <648.46g
+</code>
+and the volume group must be extended over the new NVME physical disk:
+<code bash>
+vgextend vms /dev/nvme0n1
+</code>
+Now the setup is ready for a few cache containers to be created for existing logical volumes. Assume the following LVM layout for logical volumes obtained via the ''lvs'' command:
+<code>
+  LV                         VG  Attr       LSize   Pool                     Origin                   Data%  Meta%  Move Log Cpy%Sync Convert
+  find.vm              vms -wi-a-----  20.00g
+  shinobi.vm           vms -wi-a-----  30.00g
+</code>
+where two logical volumes exist, ''find.vm'' with $20G$ storage size respectively ''shinoboi.vm'' with $20G$ storage size.
+To create a cache for ''find.vm'', first two new logical volumes are created:
+  * one logical volume acting as the actual cache,
+  * one logical volume acting as the cache metadata
+using the following commands, in order:
+<code bash>
+lvcreate -L 20G -n find.vm-cache vms /dev/nvme0n1
+</code>
+where:
+  * ''20G'' is the cache size - in this case, the cache is chosen to be the total size of the ''find.vm'' logical volume,
+  * ''find.vm-cache'' is a name for the cache volume - this can be any user-chosen name,
+  * ''vms'' is the name of the volume group containing both the slow physical disk (origin) ''/dev/sda2'' and the fast NVME physical disk ''/dev/nvme0n1'',
+  * ''/dev/nvme0n1'' is the path to the NVME physical disk
+<code bash>
+lvcreate -L 20M -n find.vm-cache-meta vms /dev/nvme0n1
+</code>
+where:
+  * ''20M'' is the size of the cache metadata logical volume - at the current time of writing, this cannot be less than ''20M'' and it is recommended to be $\frac{1}{10000}$ of the cache volume created with the previous command,
+  * ''find.vm-cache-meta'' is the name of the cache metadata logical volume - similarly to the previous command creating the cache, it can be any user chosen name,
+  * ''vms'' is the name of the volume group containing both the slow physical disk (origin) ''/dev/sda2'' and the fast NVME physical disk ''/dev/nvme0n1'',
+  * ''/dev/nvme0n1'' is the path to the NVME physical disk
+Issuing ''lvs'' at this point should reveal the cache volume and cache metadata logical volume along with the rest of the logical volumes:
+<code>
+  LV                         VG  Attr       LSize   Pool                     Origin                   Data%  Meta%  Move Log Cpy%Sync Convert
+  find.vm              vms -wi-a-----  20.00g
+  find.vm-cache        vms -wi-a-----  20.00g
+  find.vm-cache-meta   vms -wi-a-----   8.00m
+  shinobi.vm           vms -wi-a-----  30.00g
+</code>
+With the two cache and cache metadata logical volumes created, both are then combined:
+<code bash>
+lvconvert --type cache-pool --cachemode writethrough --poolmetadata vms/find.vm-cache-meta vms/find.vm-cache
+</code>
+Now, the logical volume ''find.vm'' is converted to attach the cache volume ''find.vm-cache'':
+<code bash>
+lvconvert --type cache --cachepool vms/find.vm-cache vms/find.vm
+</code>
+Issuing the ''lvs'' command should now reveal the cached logical volume:
+<code>
+  find.vm   vms Cwi-aoC---  20.00g [find.vm-cache]   [find.vm_corig]   0.42   13.11           0.00
+</code>
+Now the ''find.vm'' logical drive should be sped up by the cache.
+The result can be seen by issuing the command:
+</code bash>
+lvs -a -o +devices
+</code>
+===== Removing the Cache =====
+To remove the caching, simply delete the cache volume:
+<code bash>
+lvremove vms/find.vm-cache
+</code>
+and LVM will take care to flush the cache to the cached logical drive before removing it.