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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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2
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)

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.

10
internal/rbd/controllerserver.go
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@ -1502,6 +1502,10 @@ func (cs *ControllerServer) ControllerExpandVolume(
}, nil
}
// logThickProvisioningDeprecation makes sure the deprecation warning about
// thick-provisining is logged only once.
var logThickProvisioningDeprecation = true
// isThickProvisionRequest returns true in case the request contains the
// `thickProvision` option set to `true`.
func isThickProvisionRequest(parameters map[string]string) bool {
@ -1517,5 +1521,11 @@ func isThickProvisionRequest(parameters map[string]string) bool {
return false
}
if logThickProvisioningDeprecation {
log.WarningLogMsg("thick-provisioning is deprecated and will " +
"be removed in a future release")
logThickProvisioningDeprecation = false
}
return thickBool
}