The scenario test in the manila_tempest_tests.tests.scenario.test_share_extend module fails in two CephFS CI jobs. The failure was noted since using Ceph 18.2.4 in the CI system.

The test fails at a stage after creating a share and attempting to write past its size:

https://opendev.org/openstack/manila-tempest-plugin/src/commit/a0420244e3d14f4441adab462fe9d2a0f1316b58/manila_tempest_tests/tests/scenario/test_share_extend.py#L88-L98

The size in Ceph is a quota; and it is enforced by the ceph client rather than the server and the ceph documentation states:

"""
Once processes that write data to the file system reach the configured limit, a short period of time elapses between when the amount of data reaches the quota limit, and when the processes stop writing data. The time period generally measures in the tenths of seconds. However, processes continue to write data during that time. The amount of additional data that the processes write depends on the amount of time elapsed before they stop.
"""

So, there's possibly a sync delay where the client is able to write more data than is permitted.

Steps to reproduce
==================

• Create a CephFS share of size 1 GiB (Native or with "Standalone" NFS-Ganesha)
• Fill up the share, write past 1 GiB

Expected result
===============
You're prevented to write past 1GiB

Actual result
=============
No failure occurs; failing expectation that the size quota is enforced