[Bugs] [Bug 1257911] add policy mechanism for promotion and demotion

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1257911



--- Comment #10 from Vijay Bellur <vbellur at redhat.com> ---
COMMIT: http://review.gluster.org/12039 committed in master by Dan Lambright
(dlambrig at redhat.com) 
------
commit 672baab88fb7f32e844cd4be22e0924e4e0e83fc
Author: Dan Lambright <dlambrig at redhat.com>
Date:   Fri Sep 18 00:49:06 2015 -0400

    cluster/tier: add watermarks and policy driver

    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>

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