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docs: reference technical change detection mode section for client

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Currently, the change detection modes are described in the client
usage section, not intended for in-depth explanation on how these
client option works, but rather with focus on how to use them.
Therefore, add a reference to the more detailed technical section
regarding the change detection modes and reduce duplicate
explanations.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
Reviewed-by: Shannon Sterz <s.sterz@proxmox.com>
This commit is contained in:
Christian Ebner 2024-11-18 10:24:34 +01:00 committed by Thomas Lamprecht
parent 1964cbdaad
commit 98ac310845
1 changed files with 6 additions and 15 deletions
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docs/backup-client.rst
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@ -301,24 +301,15 @@ the client to avoid re-reading files with unchanged metadata whenever possible.
When using this mode, instead of the regular pxar archive, the backup snapshot
is stored into two separate files: the `mpxar` containing the archive's metadata
and the `ppxar` containing a concatenation of the file contents. This splitting
allows for efficient metadata lookups.
allows for efficient metadata lookups. When creating the backup archives, the
current file metadata is compared to the one looked up in the previous `mpxar`
archive. The operational details are explained more in depth in the
:ref:`technical documentation <change-detection-mode-metadata>`.
Using the `change-detection-mode` set to `data` allows to create the same split
archive as when using the `metadata` mode, but without using a previous
reference and therefore reencoding all file payloads.
When creating the backup archives, the current file metadata is compared to the
one looked up in the previous `mpxar` archive.
The metadata comparison includes file size, file type, ownership and permission
information, as well as acls and attributes and most importantly the file's
mtime, for details see the
:ref:`pxar metadata archive format <pxar-meta-format>`.
If unchanged, the entry is cached for possible re-use of content chunks without
re-reading, by indexing the already present chunks containing the contents from
the previous backup snapshot. Since the file might only partially re-use chunks
(thereby introducing wasted space in the form of padding), the decision whether
to re-use or re-encode the currently cached entries is postponed to when enough
information is available, comparing the possible padding to a threshold value.
reference and therefore reencoding all file payloads. For details of this mode
please see the :ref:`technical documentation <change-detection-mode-data>`.
.. _client_change_detection_mode_table: