From: Dominik Csapak <d.csapak@proxmox.com>
To: pbs-devel@lists.proxmox.com
Subject: [pbs-devel] [PATCH proxmox-backup v3 4/5] docs: add documentation about the 'sync-level' tuning
Date: Thu, 20 Oct 2022 09:40:57 +0200 [thread overview]
Message-ID: <20221020074058.717152-5-d.csapak@proxmox.com> (raw)
In-Reply-To: <20221020074058.717152-1-d.csapak@proxmox.com>
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
docs/storage.rst | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/docs/storage.rst b/docs/storage.rst
index 1909bd84..c4e44c72 100644
--- a/docs/storage.rst
+++ b/docs/storage.rst
@@ -338,3 +338,39 @@ and only available on the CLI:
# proxmox-backup-manager datastore update <storename> --tuning 'chunk-order=none'
+* ``sync-level``: Datastore fsync level:
+
+ You can set the level of syncing on the datastore for chunks, which influences
+ the crash resistance of backups in case of a powerloss or hard shutoff.
+ There are currently three levels:
+
+ - `none` (default): Does not do any syncing when writing chunks. This is fast
+ and normally OK, since the kernel eventually flushes writes onto the disk.
+ The kernel sysctls `dirty_expire_centisecs` and `dirty_writeback_centisecs`
+ are used to tune that behaviour, while the default is to flush old data
+ after ~30s.
+
+ - `filesystem` : This triggers a ``syncfs(2)`` after a backup, but before
+ the task returns `OK`. This way it is ensured that the written backups
+ are on disk. This is a good balance between speed and consistency.
+ Note that the underlying storage device still needs to protect itself against
+ powerloss to flush its internal ephemeral caches to the permanent storage layer.
+
+ - `file` With this mode, a fsync is triggered on every chunk insertion, which
+ makes sure each and every chunk reaches the disk as soon as possible. While
+ this reaches the highest level of consistency, for many storages (especially
+ slower ones) this comes at the cost of speed. For many users the `filesystem`
+ mode is better suited, but for very fast storages this mode can be OK.
+
+ This can be set with:
+
+.. code-block:: console
+
+ # proxmox-backup-manager datastore update <storename> --tuning 'sync-level=filesystem'
+
+If you want to set multiple tuning options simultaneously, you can separate them
+with a comma, like this:
+
+.. code-block:: console
+
+ # proxmox-backup-manager datastore update <storename> --tuning 'sync-level=filesystem,chunk-order=none'
--
2.30.2
next prev parent reply other threads:[~2022-10-20 7:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-20 7:40 [pbs-devel] [PATCH proxmox-backup v3 0/5] add 'sync-level' to datatore tuning options Dominik Csapak
2022-10-20 7:40 ` [pbs-devel] [PATCH proxmox-backup v3 1/5] docs: add information about chunk order option for datastores Dominik Csapak
2022-10-20 7:40 ` [pbs-devel] [PATCH proxmox-backup v3 2/5] pbs-datastore: chunk_store: use replace_file in insert_chunk Dominik Csapak
2022-10-20 7:40 ` [pbs-devel] [PATCH proxmox-backup v3 3/5] datastore: implement sync-level tuning for datastores Dominik Csapak
2022-10-20 13:09 ` Wolfgang Bumiller
2022-10-20 7:40 ` Dominik Csapak [this message]
2022-10-20 7:40 ` [pbs-devel] [PATCH proxmox-backup v3 5/5] datastore: make 'filesystem' the default sync-level Dominik Csapak
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