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    SubjectRe: [PATCH 00/16] DRBD: a block device for HA clusters
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    On Sat, 2009-05-02 at 22:40 -0700, david@lang.hm wrote:
    > On Sun, 3 May 2009, Willy Tarreau wrote:
    >
    > > On Sat, May 02, 2009 at 09:33:35AM +0200, Bart Van Assche wrote:
    > >> On Fri, May 1, 2009 at 10:59 AM, Andrew Morton
    > >> <akpm@linux-foundation.org> wrote:
    > >>> On Thu, 30 Apr 2009 13:26:36 +0200 Philipp Reisner <philipp.reisner@linbit.com> wrote:
    > >>>
    > >>>> This is a repost of DRBD
    > >>>
    > >>> Is it being used anywhere for anything? If so, where and what?
    > >>
    > >> One popular application is to run iSCSI and HA software on top of DRBD
    > >> in order to build a highly available iSCSI storage target.
    > >
    > > Confirmed, I have several customers who're doing exactly that.
    >
    > I will also say that there are a lot of us out here who would have a use
    > for DRDB in our HA setups, but have held off implementing it specificly
    > because it's not yet in the upstream kernel.

    Actually, that's not a particularly strong reason because we already
    have an in-kernel replicator that has much of the functionality of drbd
    that you could use. The main reason for wanting drbd in kernel is that
    it has a *current* user base.

    Both the in kernel md/nbd and drbd do sync and async replication with
    primary side bitmaps. The main differences are:

    * md/nbd can do 1 to N replication,
    * drbd can do active/active replication (useful for cluster
    filesystems)
    * The chunk size of the md/nbd is tunable
    * With the updated nbd-tools, current md/nbd can do point in time
    rollback on transaction logged secondaries (a BCS requirement)
    * drbd manages the mirror state explicitly, md/nbd needs a user
    space helper

    And probably a few others I forget.

    James




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