Bug 1306129

+++ This bug was initially created as a clone of Bug #1303895 +++

+++ This bug was initially created as a clone of Bug #1303894 +++

Description of problem:
Tests where space is created on a previously full hot-tier are showing erratic behaviour on promotions. In some runs, promotions are happening as expected. In most cases, no promotions are happening at all.

Version-Release number of selected component (if applicable):
glusterfs*-3.7.5-17.el7.x86_64
kernel: 3.10.0-327.el7.x86_64 (RHEL 7.2)

How reproducible:
Consistently, with the steps below.

Steps to Reproduce:

1. 
create 2x(8+4) base volume (about 15TB capacity); attach 2x2 SAS-SSD as hot tier (about 360GB capacity). fuse mount on a set of clients.

2. 
create directory smf_init in the mount point. create a data set of size 480GB within directory smf-init, of large files each 256MB in size. This fills up the hot tier to the max allowed.

3.
create a directory smf_data in the mount point. create a data set of size 32GB within smf_data, of small files each 64KB. rm -rf <mnt-pt>/smf_init. this deletes all files created in step 1 and creates space within the hot tier.

4. read files in the directory <mnt-pt>/smf_data. time taken for read phase is more than the promote frequency of 120s.

Actual results:
Files read in step 4. are not getting promoted to hot-tier.

Expected results:
Files should get promoted.

Additional info:

--- Additional comment from Vijay Bellur on 2016-02-02 06:17:46 EST ---

REVIEW: http://review.gluster.org/13332 (cluster/tier : Reset watermarks in tier) posted (#1) for review on master by N Balachandran (nbalacha)

--- Additional comment from Nithya Balachandran on 2016-02-02 08:45:54 EST ---

Analysis:

The tier volume in question had different nodes running the hot and cold bricks. No node contains both hot and cold bricks, so the tier process on each node will either promote or demote, but not both.

The initial create operations caused the hot tier usage to cross the high watermark configured. This was detected by the tier processes running on the cold tier nodes and tier_conf->watermark_last was set to TIER_WM_HI. 

The files on the hot tier were then deleted and the disk space freed up. The promotions are now expected to start again.

However, as the cold tier nodes do not demote files, the tier_check_watermark is not called and the watermark value is not reset. So the tier_check_promote will always fail, in turn preventing tier_watermark_check from being called .

The cold tier nodes will now never promote files and the hot tier will eventually empty out.

Such a configuration is likely to hot this issue frequently as hot tier bricks are usually small and likely to cross the high watermark frequently.

--- Additional comment from Vijay Bellur on 2016-02-02 11:47:23 EST ---

REVIEW: http://review.gluster.org/13341 (cluster/tier : Reset watermarks in tier) posted (#1) for review on master by N Balachandran (nbalacha)

--- Additional comment from Vijay Bellur on 2016-02-03 02:53:22 EST ---

REVIEW: http://review.gluster.org/13341 (cluster/tier : Reset watermarks in tier) posted (#2) for review on master by N Balachandran (nbalacha)

--- Additional comment from Vijay Bellur on 2016-02-03 12:59:29 EST ---

COMMIT: http://review.gluster.org/13341 committed in master by Dan Lambright (dlambrig) 
------
commit 545f4ed2c7195a21210e6a055c27c1b7a115e18c
Author: N Balachandran <nbalacha>
Date:   Tue Feb 2 22:09:45 2016 +0530

    cluster/tier : Reset watermarks in tier
    
    A node which contains only cold bricks and has detected that
    the high watermark value has been breached on the hot tier will
    never reset the watermark to the correct value. The promotion check
    will thus always fail and no promotions will occur from that node.
    
    Change-Id: I0f0804744cd184c263acbea1ee50cd6010a49ec5
    BUG: 1303895
    Signed-off-by: N Balachandran <nbalacha>
    Reviewed-on: http://review.gluster.org/13341
    Smoke: Gluster Build System <jenkins.com>
    NetBSD-regression: NetBSD Build System <jenkins.org>
    CentOS-regression: Gluster Build System <jenkins.com>
    Reviewed-by: Dan Lambright <dlambrig>

--- Additional comment from Vijay Bellur on 2016-02-04 08:01:58 EST ---

REVIEW: http://review.gluster.org/13357 (cluster/tier : Fixed wrong variable comparison) posted (#1) for review on master by N Balachandran (nbalacha)

--- Additional comment from Vijay Bellur on 2016-02-05 00:36:44 EST ---

REVIEW: http://review.gluster.org/13357 (cluster/tier : Fixed wrong variable comparison) posted (#2) for review on master by N Balachandran (nbalacha)