Date: Tue, 10 Dec 2002 10:44:28 +1100 From: Joshua Goodall <joshua@roughtrade.net> To: Michael Grant <mg-fbsd3@grant.org> Cc: freebsd-cluster@freebsd.org Subject: Re: sharing files within a cluster Message-ID: <20021209234428.GE98967@roughtrade.net> In-Reply-To: <200212092258.gB9Mw5l08130@splat.grant.org> References: <200212092258.gB9Mw5l08130@splat.grant.org>
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On Mon, Dec 09, 2002 at 11:58:05PM +0100, Michael Grant wrote: > I'm still stymied by the problem of how to share files across > machines without having a third (and forth!) machine acting as a > disk server. Conceptually, if you have two machines, they could act as servers for each other. There are some nasty failure modes associated with doing this, epecially if you sharing via NFS. Coda offers a more disconnected consistency model that should alleviate that somewhat. It may be beta code, but Coda itself is in production use at some large sites. > Let's say I have 2 boxes sharing the load. Each box runs a mailer. A > message could arrive at either box. How should these two mailers > share a single user's mailbox? With shared NFS mounts, the obvious answer is: use Maildirs. They are multiple-writer-safe and NFS-safe. I suggest experimenting with Coda in this scenario; particularly try an "unplug" test during delivery. > Similar problem with users who log in to their shell account, how can > they get at their files from either box? NFS cross-mounts again will do it. > Again, a similar problem with web stuff that accesses a database like > an mldbm file. Here you have a problem with locking. In the absence of a distributed lock manager, shared databases are Hard. > And for easier management, certain conf files are identical across the > machines, when modified, the one on the other machine should also get > modified. The password and aliases files comes to mind as examples, > there are pleanty more. > > The more I think about this problem, the more I become convinced that > there's definitely a need for some shared writable storage. But how? You are wanting a single-system-image cluster. Not many *nix vendors have got this right (Tru64 quite highly rated in this regard) and none of the free Unices AFAIK. Joshua -- Joshua Goodall joshua@roughtrade.net "Your byte hit ratio is weak, old man" "If you cache me now, I will dump more core than you can possibly imagine" To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-cluster" in the body of the message
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