Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 10/10/06, Dan Brown <danb at zu.com> wrote: > So I've got a couple of webservers which mirror each other without the use > of a fileserver backend. Up until now they've been using csync2 to mirror > the data between the servers and it has been working fairly well (and the > built-in file backup has come in handy once or twice as well). > > Unfortunately csync2 has a good deal of limitations as well, such as the > more files you have, the slower it is, and you can't sync more than one > server to other servers (in this case only one) at the same time. I'm > running it in a master/master mode. Overall it was designed to be more of a > tool to update configs, or update relatively non-interactive systems. > > So recently I've been looking more and more at DRBD and NFS (before I spend > a couple of grand on a well built fileserver). So what I am looking at is > something like this: > > server A (DRBD + active NFS) > + mounted by itself and server B > > server B (DRBD + disabled NFS) > + mounts server A NFS share > > So while server A is the active NFS server and server B is passive and only > synching, both servers would mount via NFS server A. When server A goes > down for whatever reason (reboot, crash, etc) server B will take over and > continue where server A left off. One thing I keep seeing in various > documents however is a warning not to have the server mount its own NFS > shares. There is never reason (even a vague reason) given why not to > however. I can see the obvious reasons (eg. infinitely nested filesystems > via symlinks/mounts, crossmounts, etc), but my directory structures should > not need anything like this at all. Other than overall system complexity, > I don't see any reasons to not be able to self mount NFS with a whole lot of > trouble. Odd -- the NFS-HA howto shows how to do exactly this. Also: we've deployed this for mail and web without issues this far, albeit, in a non-complex environment. > The problems I see include Apache log files (I'd assume each server would > have to write to separate logs), Absolutely. > and what happens when the servers > disconnect from each other (eg. NIC failure) but are both still active and > both decide they are masters. How are synchronization issues then resolved? You generally run a serial cable between the nodes to prevent a split brain and not rely entirely on network. -- Mustafa A. Hashmi mahashmi at gmail.com mh at stderr.net