From mboxrd@z Thu Jan 1 00:00:00 1970
Return-Path: <pbs-devel-bounces@lists.proxmox.com>
Received: from firstgate.proxmox.com (firstgate.proxmox.com [212.224.123.68])
by lore.proxmox.com (Postfix) with ESMTPS id 1F0A01FF389
for <inbox@lore.proxmox.com>; Tue, 7 May 2024 17:54:30 +0200 (CEST)
Received: from firstgate.proxmox.com (localhost [127.0.0.1])
by firstgate.proxmox.com (Proxmox) with ESMTP id 791A01297C;
Tue, 7 May 2024 17:54:21 +0200 (CEST)
From: Christian Ebner <c.ebner@proxmox.com>
To: pbs-devel@lists.proxmox.com
Date: Tue, 7 May 2024 17:52:35 +0200
Message-Id: <20240507155244.793819-54-c.ebner@proxmox.com>
X-Mailer: git-send-email 2.39.2
In-Reply-To: <20240507155244.793819-1-c.ebner@proxmox.com>
References: <20240507155244.793819-1-c.ebner@proxmox.com>
MIME-Version: 1.0
X-SPAM-LEVEL: Spam detection results: 0
AWL 0.027 Adjusted score from AWL reputation of From: address
BAYES_00 -1.9 Bayes spam probability is 0 to 1%
DMARC_MISSING 0.1 Missing DMARC policy
KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment
SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record
SPF_PASS -0.001 SPF: sender matches SPF record
Subject: [pbs-devel] [PATCH v5 proxmox-backup 53/62] docs: add section
describing change detection mode
X-BeenThere: pbs-devel@lists.proxmox.com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Proxmox Backup Server development discussion
<pbs-devel.lists.proxmox.com>
List-Unsubscribe: <https://lists.proxmox.com/cgi-bin/mailman/options/pbs-devel>,
<mailto:pbs-devel-request@lists.proxmox.com?subject=unsubscribe>
List-Archive: <http://lists.proxmox.com/pipermail/pbs-devel/>
List-Post: <mailto:pbs-devel@lists.proxmox.com>
List-Help: <mailto:pbs-devel-request@lists.proxmox.com?subject=help>
List-Subscribe: <https://lists.proxmox.com/cgi-bin/mailman/listinfo/pbs-devel>,
<mailto:pbs-devel-request@lists.proxmox.com?subject=subscribe>
Reply-To: Proxmox Backup Server development discussion
<pbs-devel@lists.proxmox.com>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: pbs-devel-bounces@lists.proxmox.com
Sender: "pbs-devel" <pbs-devel-bounces@lists.proxmox.com>
Describe the motivation and basic principle of the clients change
detection mode and show an example invocation.
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 4:
- no changes
docs/backup-client.rst | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/docs/backup-client.rst b/docs/backup-client.rst
index 00a1abbb3..e48b5dd60 100644
--- a/docs/backup-client.rst
+++ b/docs/backup-client.rst
@@ -280,6 +280,47 @@ Multiple paths can be excluded like this:
# proxmox-backup-client backup.pxar:./linux --exclude=/usr --exclude=/rust
+.. _client_change_detection_mode:
+
+Change detection mode
+~~~~~~~~~~~~~~~~~~~~~
+
+File-based backups containing a lot of data can take a long time, as the default
+behavior for the Proxmox backup client is to read all data and re-encode it.
+The encoded stream is split into variable sized chunks for efficient
+deduplication and based on the chunk digest a decision can be made whether a
+given chunk needs to be uploaded or can be indexed without upload as it is
+already available on the server (and therefore deduplicated). For some
+use-cases, where files do not change frequently the full re-reading is not
+feasible and undesired.
+
+The backup clients `change-detection-mode` can be switched from default to
+`metadata` based detection to reduce limitations as described above, instructing
+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 archives metadata
+and the `ppxar` containing a concatenation of the file contents. This splitting
+allows for metadata lookups without the overhead of the file contents.
+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, and if unchanged the entry 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 delegated to when enough information
+is available, comparing the possible padding a threshold value.
+
+The following shows an example for the client invocation with the `metadata`
+mode:
+
+.. code-block:: console
+
+ # proxmox-backup-client backup.pxar:./linux --change-detection-mode=metadata
+
.. _client_encryption:
Encryption
--
2.39.2
_______________________________________________
pbs-devel mailing list
pbs-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pbs-devel