[pbs-devel] [PATCH v2 proxmox-backup 2/2] docs: deduplicate background details for garbage collection

[Gabriel Goller]

On 13.11.2024 16:55, Christian Ebner wrote:
>diff --git a/docs/maintenance.rst b/docs/maintenance.rst
>index e8a26d69c..bba3feff4 100644
>--- a/docs/maintenance.rst
>+++ b/docs/maintenance.rst
>@@ -197,6 +197,8 @@ It's recommended to setup a schedule to ensure that unused space is cleaned up
> periodically. For most setups a weekly schedule provides a good interval to
> start.
>
>+.. _gc_background:
>+
> GC Background
> ^^^^^^^^^^^^^
>
>@@ -222,17 +224,31 @@ datastore or interfering with other backups.
> The garbage collection (GC) process is performed per datastore and is split
> into two phases:
>
>-- Phase one: Mark
>-  All index files are read, and the access time of the referred chunk files is
>-  updated.
>-
>-- Phase two: Sweep
>-  The task iterates over all chunks, checks their file access time, and if it
>-  is older than the cutoff time (i.e., the time when GC started, plus some
>-  headroom for safety and Linux file system behavior), the task knows that the
>-  chunk was neither referred to in any backup index nor part of any currently
>-  running backup that has no index to scan for. As such, the chunk can be
>-  safely deleted.
>+- Phase one (Mark):
>+
>+  All index files are read, and the access time (``atime``) of the referenced
>+  chunk files is updated.
>+
>+- Phase two (Sweep):
>+
>+  The task iterates over all chunks and checks their file access time against a
>+  cutoff time. The cutoff time is given by either the oldest backup writer
>+  instance, if present, or 24 hours and 5 minutes after the start of garbage
>+  collection.
>+

>+  Garbage collection can consider chunk files with access time older than the

s/can consider/considers/
It always considers chunks with atime older than cutoff to be dangling
afaik.

>+  cutoff time to be neither referenced by any backup snapshot's index, nor part
>+  of any currently running backup job. Therefore, these chunks can safeley be
>+  deleted.

s/safeley/safely/

>+
>+  Chunks within the grace period will not be deleted and logged at the end of
>+  the garbage collection task as *Pending removals*.
>+
>+.. note:: The grace period for backup chunk removal is not arbitrary, but stems
>+   from the fact that filesystems are typically mounted with the ``relatime``
>+   option by default. This results in better performance by only updating the
>+   ``atime`` property if a file has been modified since the last access or the
>+   last access has been at least 24 hours ago.
>
> Manually Starting GC
> ^^^^^^^^^^^^^^^^^^^^

Otherwise this is great!