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We are having to migrate a web server hosting a subversion repository via mod_dav_svn to a new machine and host name. To ease transition, we are looking at running the two web servers in parallel with repository NFS mounted on both at the same time. We can then progressively do a 'svn switch' on checked out working copies to new host name.

The concern is that each mod_dav_svn is a different version. The older is 1.3 and the newer is 1.6. Further, the actual repository (db/format) is '1', so potentially wasn't ever upgraded when we went to 1.3.

The release notes for 1.5 and 1.6 both say words to the effect:

Repository Upgrades - The Subversion 1.6 server works with 1.5 and older repositories, and it will not upgrade such repositories to 1.6 unless specifically requested to via the svnadmin upgrade command. This means that some of the new 1.6 features will not become available simply by upgrading your server: you will also have to upgrade your repositories. (We decided not to auto-upgrade repositories because we didn't want 1.6 to silently make repositories unusable by 1.5 — that step should be a conscious decision on the part of the repository admin.)

Also, since the repository format is still '1' even though using 1.3, then likely that the same applied to 1.3 as well.

So it doesn't look like there is any risk of 1.6 upgrading the repository and making it unusable to 1.3 at the same time. This will allow us to do our migrations and when we are done and old server shutdown, then we can do the 'svnadmin upgrade' on the repository to get it up to 1.6 and get access to any new features provided clients also 1.6.

Can anyone see any issues with this plan?

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This seems like more work than it's worth. Why not just migrate the repository to the new server and include a basic 2-3 line proxy config on the old server for the transition period?

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Running in parallel allows us to test properly that the new system works before cutting over without disrupting existing users. We also have added complexity of changing authentication database when we swap from a htpasswd database to LDAP. Usernames and passwords in this new user database aren't necessarily the same and rather than switch to a proxy arrangement and have everything break immediately for all users, can gradually assist sizable number of users to migrate gradually. It also isn't a case of a single project in the subversion repository but rather hundreds so have to be careful. –  Graham Dumpleton Jul 29 '10 at 9:42
    
Fair enough. I guess I've been spoiled by not having to deal with any non-synchronized authentication systems in a long time. Sorry I can't address the actual compatibility issue - I've never tried multiple servers on a repository before. I'd guess as long as NFS file locking is set up properly it has a good chance though. –  Jeremy M Jul 30 '10 at 1:11

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