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doc/rbd: change persistent write-back cache to persistent write log cache

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The full name of PWL is persistent write log, and the full name of
RWL is replica write log. Change the title to make it consistent
with the name of the feature and better reflect its design.

Signed-off-by: Yin Congmin <congmin.yin@intel.com>
This commit is contained in:
Yin Congmin 2021-12-01 14:37:50 +08:00
parent b1d712d29d
commit 1b4f4841bb
2 changed files with 18 additions and 17 deletions
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2
doc/rbd/rbd-operations.rst
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@ -10,7 +10,7 @@
Mirroring <rbd-mirroring>
Live-Migration <rbd-live-migration>
Persistent Read-only Cache <rbd-persistent-read-only-cache>
Persistent Write-back Cache <rbd-persistent-write-back-cache>
Persistent Write Log Cache <rbd-persistent-write-log-cache>
Encryption <rbd-encryption>
Config Settings (librbd) <rbd-config-ref/>
RBD Replay <rbd-replay>

33
doc/rbd/rbd-persistent-write-back-cache.rst → doc/rbd/rbd-persistent-write-log-cache.rst
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@ -1,32 +1,34 @@
================================
RBD Persistent Write-back Cache
RBD Persistent Write Log Cache
================================
.. index:: Ceph Block Device; Persistent Write-back Cache
.. index:: Ceph Block Device; Persistent Write Log Cache
Persistent Write-back Cache
Persistent Write Log Cache
===========================
The persistent write-back cache provides a persistent, fault-tolerant write-back
cache for librbd-based RBD clients.
The Persistent Write Log Cache (PWL) provides a persistent, fault-tolerant
write-back cache for librbd-based RBD clients.
This cache uses a log-ordered write-back design which maintains checkpoints
internally so that writes that get flushed back to the cluster are always
crash consistent. Even if the client cache is lost entirely, the disk image is
still consistent but the data will appear to be stale.
This cache can be used with PMEM or SSD as a cache device.
This cache can be used with PMEM or SSD as a cache device. For PMEM, the cache
mode is called ``replica write log (rwl)``. At present, only local cache is
supported, and the replica function is under development. For SSD, the cache
mode is called ``ssd``.
Usage
=====
The persistent write-back cache manages the cache data in a persistent device.
It looks for and creates cache files in a configured directory, and then caches
data in the file.
The PWL cache manages the cache data in a persistent device. It looks for and
creates cache files in a configured directory, and then caches data in the
file.
The persistent write-back cache can't be enabled without the exclusive-lock
feature. It tries to enable the write-back cache only when the exclusive lock
is acquired.
The PWL cache depends on the exclusive-lock feature. The cache can be loaded
only after the exclusive lock is acquired.
The cache provides two different persistence modes. In persistent-on-write mode,
the writes are completed only when they are persisted to the cache device and
@ -38,11 +40,10 @@ The data is persisted to the cache device when a flush request is received.
Initially it defaults to the persistent-on-write mode and it switches to
persistent-on-flush mode after the first flush request is received.
Enable Persistent Write-back Cache
Enable Cache
========================================
To enable the persistent write-back cache, the following Ceph settings
need to be enabled.::
To enable the PWL cache, set the following configuration settings::
rbd persistent cache mode = {cache-mode}
rbd plugins = pwl_cache
@ -71,7 +72,7 @@ set per-host, add the overrides to the appropriate `section`_ in the host's
Cache Status
------------
The persistent write-back cache is enabled when the exclusive lock is acquired,
The PWL cache is enabled when the exclusive lock is acquired,
and it is closed when the exclusive lock is released. To check the cache status,
users may use the command ``rbd status``. ::