Turning off atime on a filesystem

I am setting up a mongoDB replica set and one of the first things I am suppose to do is turn off atime on the file system. After researching this a bit, I am not opposed to doing this, but I have to ask, what uses atime? I have searched the interwebs and found very little in the way of "this applciaiton or this process uses atime and you would be stupid if you turned it off" kinds of warnings, but being a paranoid person by nature, I have to wonder.

So, what uses atime and if I turn it off, what could break?

mutt, an email client, uses file access times to monitor for new mail arriving on an mbox-formatted mailbox. Apparently, this problem is not serious, and is easy to work around.

Other than that, it is difficult to find examples of things that break on noatime. I run a number of Linux servers with noatime on all filesystems, and I can't recall ever having seen any problems attributable to noatime.

If you are concerned about using noatime in general, you could devote a separate filesystem for your mongoDB stuff, and mount only that filesystem with noatime.

EDIT

I found an interesting blog at kerneltrap.org that quotes some discussions between Linux developers (Linus Torvalds, Ingo Molnar, Alan Cox, and others) on the topic of atime. In Ingo's second email, he says this:

... i've got no real complaint about ext3 - with the obligatory qualification that "noatime,nodiratime" in /etc/fstab is a must. This speeds up things very visibly - especially when lots of files are accessed. It's kind of weird that every Linux desktop and server is hurt by a noticeable IO performance slowdown due to the constant atime updates, while there's just two real users of it: tmpwatch [which can be configured to use ctime so it's not a big issue] and some backup tools. (Ok, and mail-notify too i guess.) Out of tens of thousands of applications. So for most file workloads we give Windows a 20%-30% performance edge, for almost nothing.

Tools that poll for file usage such as temporary file cleaners use it. You can get around this on some filesystems and OSes by using relatime instead, which only updates the atime after a certain duration has passed since it was last updated.

You could also create a seperate mount point for your mongoDB replica set. You can then set the noatime paramtere on that mountpoint only without affecting any other programs.