Comment 4 for bug 1336568

Reviewed: https://review.openstack.org/104714
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=617e59bde660f919df0818611b911ae35f8b7247
Submitter: Jenkins
Branch: master

commit 617e59bde660f919df0818611b911ae35f8b7247
Author: Mitsuhiro Tanino <email address hidden>
Date: Tue Jul 8 15:52:11 2014 -0400

    Configure write cache option of tgtd iscsi driver

    Cinder LVMiSCSI driver is using default value of write-cache parameter
    of tgtd iscsi driver. In this setting, write I/O from guest instance is
    cached on dirty cache of a host.(write-back mode)

    In this case, data lost may be occurred if the host crashes before
    flushing dirty cache. This may cause a lot of instances to lose
    their data.

    In order to avoid this issue, it is better to turn off the write cache.
    (write-through mode)

    This patch adds "iscsi_write_cache" parameter to configure a behavior of
    write cache. The default value is "iscsi_write_cache=on".(write-back mode)

    Closes-Bug: 1336568
    DocImpact

    Change-Id: I7a495bc6118d4254576bdf1620a04ac537b3078d
    Signed-off-by: Mitsuhiro Tanino <email address hidden>