[Bugs] [Bug 1270527] add policy mechanism for promotion and demotion

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1270527



--- Comment #2 from Vijay Bellur <vbellur at redhat.com> ---
COMMIT: http://review.gluster.org/12330 committed in release-3.7 by Dan
Lambright (dlambrig at redhat.com) 
------
commit 98fa496c211dc0da7bccb68fc57f97d835e56c28
Author: Dan Lambright <dlambrig at redhat.com>
Date:   Fri Sep 18 00:49:06 2015 -0400

    cluster/tier: add watermarks and policy driver

    Backport fix 12039

    This fix introduces infrastructure to support different
    policies for promotion and demotion.

    Currently the tier feature automatically promotes and demotes
    files periodically based on access. This is good for testing
    but too stringent for most real workloads. It makes it
    difficult to fully utilize a hot tier- data will be demoted
    before it is touched- its unlikely a 100GB hot SSD will have
    all its data touched in a window of time.

    A new parameter "mode" allows the user to pick promotion/demotion
    polcies.

    The "test mode" will be used for *.t and other general testing.
    This is the current mechanism.

    The "cache mode" introduces watermarks. The watermarks
    represent levels of data residing on the hot tier.

    "cache mode" policy:

    The % the hot tier is full is called P.

    Do not promote or demote more than D MB or F files.

    A random number [0-100] is called R.

    Rules for migration:

    if (P < watermark_low) don't demote, always promote.

    if (P >= watermark_low) && (P < watermark_hi) demote if R < P; promote if R
> P.

    if (P > watermark_hi) always demote, don't promote.

    gluster volume set {vol} cluster.watermark-hi %
    gluster volume set {vol} cluster.watermark-low %
    gluster volume set {vol} cluster.tier-max-mb {D}
    gluster volume set {vol} cluster.tier-max-files {F}
    gluster volume set {vol} cluster.tier-mode {test|cache}

    > Change-Id: I157f19667ec95aa1d53406041c1e3b073be127c2
    > BUG: 1257911
    > Signed-off-by: Dan Lambright <dlambrig at redhat.com>
    > Reviewed-on: http://review.gluster.org/12039
    > Tested-by: Gluster Build System <jenkins at build.gluster.com>
    > Reviewed-by: Atin Mukherjee <amukherj at redhat.com>
    Signed-off-by: Dan Lambright <dlambrig at redhat.com>

    Signed-off-by: Dan Lambright <dlambrig at redhat.com>

    Conflicts:
        xlators/cluster/dht/src/dht-rebalance.c
        xlators/cluster/dht/src/tier.c

    Change-Id: Ibfe6b89563ceab98708325cf5d5ab0997c64816c
    BUG: 1270527
    Reviewed-on: http://review.gluster.org/12330
    Tested-by: NetBSD Build System <jenkins at build.gluster.org>
    Tested-by: Gluster Build System <jenkins at build.gluster.com>
    Reviewed-by: Dan Lambright <dlambrig at redhat.com>
    Tested-by: Dan Lambright <dlambrig at redhat.com>

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