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docs: fix #2851 Add note about GC grace period

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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@proxmox.com>
This commit is contained in:
Aaron Lauterer 2020-07-21 11:54:35 +02:00 committed by Thomas Lamprecht
parent 538c2b6dcf
commit 8314ca9c10
1 changed files with 11 additions and 0 deletions
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docs/administration-guide.rst
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@ -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