[pbs-devel] [PATCH proxmox-backup 1/3] docs: fix #2851 Add note about GC grace period
Aaron Lauterer
a.lauterer at proxmox.com
Tue Jul 21 11:54:35 CEST 2020
Adding a note about the garbage collection's grace period due to the
default atime behavior should help to avoid confusion as to why space is
not freed immediately.
Signed-off-by: Aaron Lauterer <a.lauterer at proxmox.com>
---
I hope I got the technical details right.
I did put the section in a note for now but I am not sure if it is the
best way to present that information.
docs/administration-guide.rst | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/docs/administration-guide.rst b/docs/administration-guide.rst
index 254d36e1..a0ac8c79 100644
--- a/docs/administration-guide.rst
+++ b/docs/administration-guide.rst
@@ -962,6 +962,17 @@ unused data blocks are removed.
depending on the number of chunks and the speed of the underlying
disks.
+.. note:: The garbage collection will only remove chunks that haven't been used
+ for at least one day (exactly 24h 5m). This grace period is necessary because
+ chunks in use are marked by touching the chunk which updates the ``atime``
+ (access time) property. Filesystems are mounted with the ``relatime`` option
+ by default. This results in a better performance by only updating the
+ ``atime`` property if the last access has been at least 24 hours ago. The
+ downside is, that touching a chunk within these 24 hours will not update its
+ ``atime`` property.
+
+ If there are chunks in the grace period, it will be logged at the end of the
+ garbage collection run as *Pending removals*.
.. code-block:: console
--
2.20.1
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