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Re: [Linux-cluster] GFS on AOE



Jeff Sturm wrote:
-----Original Message-----
From: linux-cluster-bounces redhat com
[mailto:linux-cluster-bounces redhat com]
On Behalf Of Fabio M. Di Nitto
Sent: Tuesday, December 07, 2010 5:42 AM
To: linux-cluster redhat com
Subject: Re: [Linux-cluster] GFS on AOE

The problem being that AOE (as you suspect) adds a different level of
caching.

Note however that the AoE protocol does not specify caching, except for
optional asynchronous writes.  (The aoe Linux module does not utilize
asynchronous writes.)

It's still an unusual setup. Rather than use a lopsided setup of one node using the disk directly and the other via AoE, it would probably be safer and more reasonable to have the physical disk only accessed by the AoE server daemon and have both nodes connect to that..

Nevertheless, the configuration suggested by the OP is unusual, and
won't be very useful in my opinion.  Having node B rely on a hard disk
in node A leaves node A as a single point of failure.

Arguably a "proper" SAN would also be a SPOF itself - unless you have two mirrored in real-time.

DRBD is good for a "poor man's SAN" that does away with the SPOF, unlike most "enterprise grade" SANs that are based on the assumption that the SAN will never fail.

Gordan


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