Niels de Vos b132696e54 rbd: note that thick-provisioning is deprecated
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>
2021-10-27 06:54:07 +00:00
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