Using an automounter doesn't always help with bad NFS servers

March 14, 2015

Suppose, not entirely hypothetically, that you have a NFS fileserver that is locking up every so often, that you statically mount its filesystems on your IMAP server, your mail server, your general login server, your web server, and so on, and that as a result when it locks up many of your servers wind up grinding to a halt. Clearly the workaround is to switch from static NFS mounts to an automounter, right?

Not so fast. Switching from static NFS mounts to using an automounter probably won't help you here. The problem is that an automounter only helps with inactive, rarely used filesystems, because these are the only sort of filesystems that it doesn't have mounted. If you have machines that are naturally using these filesystems all the time, as people read their email and serve up their home pages and so on, there's no practical difference between an automounter setup and static NFS mounts. The filesystems are mounted and active all the time and the moment the NFS fileserver goes away you're going to start have problems, as process after process tries to read from them and stalls out.

(In this situation all that switching to an automounter will do is add more moving parts to your system.)

An automounter is a decent solution to unreliable but infrequently used NFS servers, which is the situation it was designed for. It's unfortunately not a particularly effective way to deal with frequently used fileservers that become unreliable, but then nothing is; if you need filesystems and they're not responding, you have problems no matter what.

(You only have two real solutions: make your fileservers reliable or make as many machines as possible not need filesystems from the unreliable fileservers. The latter may require extreme measures like multiple IMAP servers, each one of which only talks to one fileserver.)

Comments on this page:

By Robert at 2015-03-14 13:20:35:

I would like to add that an automounter's use case is not only for unreliable servers but also for a centrally managed configuration. Or even lack of it when you run the feature and automount every NFS-server under /net.

By cks at 2015-03-14 17:03:28:

There are many ways to get a centrally managed NFS mount configuration; the automounter is only the most obvious. For example we wrote own system for this.

Written on 14 March 2015.
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Last modified: Sat Mar 14 00:41:14 2015
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