Re: [vserver] Poll: High (ish) availability - how are you doing it?

From: Edward Capriolo <edlinuxguru_at_gmail.com>
Date: Sat 31 Jul 2010 - 20:52:26 BST
Message-ID: <AANLkTimP171ywxkM5Vp2GCRzd_gGZtxW9BXU_bEQ7yo3@mail.gmail.com>

On Fri, Jul 30, 2010 at 5:19 AM, Jeff Jansen <jeff.jansen@kkoncepts.net> wrote:
> Eugen Leitl <eugen@leitl.org> wrote on 2010-Jul-28:
>> Please do; I would be also quite interested as well.
>
> OK, my first pass at "HA Vserver with DRBD and Heartbeat" docs are up at:
>
> http://www.kkoncepts.net/HA
>
> Comments are enabled, so you can comment on the page if you've got suggestions,
> corrections, clarifications, etc.
>
> Jeff Jansen
>

>> It does not scale as well as some other solutions, but it may have other advantages that you want (maybe better locking, maybe >>better fail over support...).

A little off topic, but it is important distinction between scaling
and fail over. You really have to think hard on what your looking for.

DRBD gives you disk replication Active/Passive and Active/Active 2
nodes. Active Passive does not scale and active/active "scales" to two
nodes which really is not scaling, in best case if you scaled a web
server now you can handle twice the traffic, what happens when you get
three or ten times the traffic? That solution no longer holds up.

A two node active/passive ext3 on top of DRBD managed by hearbeat (or
whatever) is not a scaling solution, its just a high availability
solution.

At this point you have to look into file systems that allow multiple
read/writes NFS or OCFS2. NFS does have locking but
it seems to be the general case that no one was any luck with it in
high contention situations.
http://cyrusimap.web.cmu.edu/imapd/faq.html.

OCFS2 is multi-attach file systems and it supports much stronger
locking semantics. Great! now that we have good locks and multi-mount
the question becomes what software is designed to work with this type
of file system? Can we have 10 nodes running mysql and
managing/working with the same MYD tables? It may work in theory but
practically I do not know of anyone doing it?

http://forums.mysql.com/read.php?144,205829,205829

The only software I know of that works well and scales on OCFS2 is
oracle, (probably because oracle corporation made both)

Most prominent scaling solutions cassandra, hbase, mongo, redis, hdfs.
Do NOT work with multi-attached file systems.
Received on Sat Jul 31 20:52:47 2010

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