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rbd: note that thick-provisioning is deprecated

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Thick-provisioning was introduced to make accounting of assigned space
for volumes easier. When thick-provisioned volumes are the only consumer
of the Ceph cluster, this works fine. However, it is unlikely that this
is the case. Instead, accounting of the requested (thin-provisioned)
size of volumes is much more practical as different types of volumes can
be tracked.

OpenShift already provides cluster-wide quotas, which can combine
accounting of requested volumes by grouping different StorageClasses.

In addition to the difficult practise of allowing only thick-provisioned
RBD backed volumes, the performance makes thick-provisioning
troublesome. As volumes need to be completely allocated, data needs to
be written to the volume. This can take a long time, depending on the
size of the volume. Provisioning, cloning and snapshotting becomes very
much noticeable, and because of the additional time consumption, more
prone to failures.

Signed-off-by: Niels de Vos <ndevos@redhat.com>
This commit is contained in:
Niels de Vos
2021-10-25 15:05:33 +02:00
committed by mergify[bot]
parent 0838845c6a
commit b132696e54
3 changed files with 15 additions and 4 deletions
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docs/deploy-rbd.md
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@ -64,7 +64,7 @@ make image-cephcsi
| `mounter` | no | if set to `rbd-nbd`, use `rbd-nbd` on nodes that have `rbd-nbd` and `nbd` kernel modules to map rbd images |
| `encrypted` | no | disabled by default, use `"true"` to enable LUKS encryption on PVC and `"false"` to disable it. **Do not change for existing storageclasses** |
| `encryptionKMSID` | no | required if encryption is enabled and a kms is used to store passphrases |
| `thickProvision` | no | if set to `"true"`, newly created RBD images will be completely allocated by writing zeros to it |
| `thickProvision` | no | if set to `"true"`, newly created RBD images will be completely allocated by writing zeros to it (**DEPRECATED**: recommended alternative solution is to use accounting/quotas for created volumes) |
**NOTE:** An accompanying CSI configuration file, needs to be provided to the
running pods. Refer to [Creating CSI configuration](../examples/README.md#creating-csi-configuration)