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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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7
examples/rbd/storageclass.yaml
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@ -29,9 +29,10 @@ parameters:
# eg: pool: rbdpool
pool: <rbd-pool-name>
# Set thickProvision to true if you want RBD images to be fully allocated on
# creation (thin provisioning is the default).
thickProvision: "false"
# Deprecated: Set thickProvision to true if you want RBD images to be fully
# allocated on creation (thin provisioning is the default).
# thickProvision: "false"
# (required) RBD image features, CSI creates image with image-format 2
# CSI RBD currently supports `layering`, `journaling`, `exclusive-lock`
# features. If `journaling` is enabled, must enable `exclusive-lock` too.