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Re: multiple svn front-ends, single SAN repo volume

From: Blair Zajac <blair_at_orcaware.com>
Date: Sat, 11 Feb 2012 22:50:37 -0800

On 2/10/2012 10:21 AM, Bruce Lysik wrote:
> Hi,
>
> I'm considering deploying 3 front-ends, all mounting the same SAN volume
> for repo. (The SAN handle flock() and fnctl() correctly.) These 3 FEs
> would be load balanced by a Citrix Netscaler. (At least for http(s).)

The largest issues I've run into using a shared storage is not the
flock() and fcntl() but the atomic renames. fsfs will atomically rename
three files to do a commit and the last rename of the 'current' file, on
some shared filesystems, will result in points of time where the systems
not doing a commit will not see a 'current' file. If this happens, then
any svn read or write operation on the repository will temporarily fail.

We had GPFS and it never failed to implement the posix requirements, but
it was slow for the number of commits we were pushing (6/sec), so we
ended up going to a single server solution with a standby. There was
another filesystem, I forgot its name, which didn't implement atomic
renames correctly and wasn't usable for svn.

Have you tested your SAN deployment?

What I would do is create a fsfs repository and on one of your hosts, do
as many commits per second as you can in a tight loop, then have another
host in a tight loop do an operation on the repository, like get the log
message of the HEAD revision.

If you want to test your flock() and fcntl() and see how well that
performs, try to do as many commits per second into the same repo from
two or more hosts. In this case, have a repository with N directories
and have each host modify a file in a single directory, that way you
won't get any conflicts.

How many commits per second are you expecting in practice?

Blair

--
Blair Zajac, Ph.D.
CTO, OrcaWare Technologies
<blair_at_orcaware.com>
Subversion training, consulting and support
http://www.orcaware.com/svn/
Received on 2012-02-12 07:51:35 CET

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