Re: what's the current wisdom on git over NFS/CIFS?

On Fri, Jul 3, 2009 at 2:28 AM, Linus
Torvalds[off-list ref] wrote:

On Thu, 2 Jul 2009, Sitaram Chamarty wrote:

quoted

A couple of us were beating each other senseless on this
issue over on #git, so I thought I'd ask: is it OK to do
this?  Or would there potential be race conditions due to
the lack of proper locking?

It should all work fine.

We've had a few NFS issues due to oddities with renaming across
directories, but modern git avoids the cross-directory renames, and that
whole issue only hit some very specific cases anyway.

And git doesn't have "proper locking", because it doesn't need it for
database ops: git objects are stable. For refs, git should be using the
proper NFS-safe "create and atomic rename" ops.

You do need to be a bit careful if you do maintenance operations
concurrently (I would suggest avoiding doing concurrent "git gc --prune",
for example), but any normal git workflow should be fine.

There is one big thing to look out for: performance. You may want to add

       [core]
               PreloadIndex = true

Great!  Thanks for the really detailed reply; appreciate it very much.

I knew about core.PreloadIndex simply due to searching "man
git-config" for NFS etc., but not the rest of it.

in your .git/config file, especially if you have a high-latency NFS server
(but if you have a fast network and a high-end NFS server, you might be
better off without it, so do your own testing).

Btw, I think we fixed the problem we had with CIFS. That one was a cifs
filesystem problem on Linux, but it should be fixed in 2.6.30+ (commit
0f4d634c: "cifs: flush data on any setattr"). If you have an older kernel
(or are just uncertain), you can also work around it with

       [core]
               fsyncobjectfiles = true

which may be a good thing in general (regardless of any cifs issues), but
in most cases the performance loss isn't worth it if your filesystem is
stable and sane.

Though I asked this following from a debate on IRC, it now looks as if
this will solve another of my problems too.

Let me explain.

I'm evangelising git at work, and although most projects are happy,
even eager to setup a proper server for git, and those that can't are
happy to just use mine, there are a couple of projects that are almost
exclusively Windows _and_ cannot add another machine _and_ have client
confidentiality issues so they can't just use my server.

My alternatives for them so far were (1) VirtualBox running Fedora or
something within one of their beefier Windows servers or (2) the whole
cygwin install, which is painful compared to msysgit.

Sounds like we can just do it with traditional Windows fileshares, as
long as we make sure no one does a "git gc" on the bare repo that is
being shared.  That's a very small price to pay!

Thanks once again, and I'm copying Gitte in case he has anything to
add, seeing I have sneakily changed the focus of the question now :-)
[It wasn't pre-meditated, honest!]

Sitaram