Re: [PATCH 00/23] per device dirty throttling -v8

Ingo Molnar
2007-08-05T07:28:40Z

* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> > Can you give examples of backup solutions that rely on atime being
> > updated? I can understand backup tools using mtime/ctime for
> > incremental backups (like tar + Amanda, etc), but I'm having trouble
> > figuring out why someone would want to use atime for that.
>
> HSM is the usual one, and to a large extent probably why Unix
> originally had atime. Basically migrating less used files away so as
> to keep the system disks tidy.

atime is used as a _hint_, at most and HSM sure works just fine on an
atime-incapable filesystem too. So it's the same deal as "add user_xattr
mount option to the filesystem to make Beagle index faster". It's now:
"if you use HSM storage add the atime mount option to make it slightly
more intelligent. Expect huge IO slowdowns though."

The only remotely valid compatibility argument would be Mutt - but even
that handles it just fine. (we broke way more software via noexec)

Ingo