Mark, you are wrong. You CAN (and even SHOULD) use controller in write-back
mode with the cluster -
any such controller have a power-independent memory and syncronize cache
between cluster nodes (if SAN itself is a cluster).
Running SAN systems in Write-thru mode degrade performance dramatically
(sometimes 2 - 10 times) and can be recommended
only for super-mission-critical tasks (because such systems have a danger of
losing inromation, if they lost power for more then a few days so that
batteries can't hold cache long enough - typical time is 72 hours).
Cash works AFTER all Linux nodes connects to the controller, so it is
transparent for the controller (but it can create a jitter in writing time,
true).
On Wed, Aug 15, 2007 at 05:43:14PM -0700, Ulf Zimmermann wrote:
The SAN is a 3Par E200, which does write into cache on its two
controllers, then acknowledges a write and then writes it actually to
disk. I have not found any reason for this delay yet, so sofar I am
stumped why it had such a long delay writing.
Are you saying that the controllers are doing write-back caching? If
they're
in that sort of mode, you need to change it to write-through for a
clustered
environment.
--Mark
--
Mark Fasheh
Senior Software Developer, Oracle
[EMAIL PROTECTED]
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