Disabling atime

[Bill Crawford]

On 21/08/07, Eric Sandeen <esandeen at redhat.com> wrote:

> I have at least one case where noatime actually slows things down.  With
> 66 million inodes on an ext3 filesystem, "find" across the filesystem
> with a fresh mount / cold cache was a few seconds slower with noatime.
> Odd result, but it shows at least that this change shouldn't be made
> based on a hunch, but only after looking at some real results.

It's mainly of benefit where the atime updates would interleave with
read traffic on the same disk, thus causing extra seeks, for example.
Experiential (yeah, I know :)) evidence is that when there's a fair
amount of disk traffic anyway, things like recursive grep or find
finish faster, but also *other things* go faster when run at the same
time. An isolated "benchmark" such as yours never shows this sort of
effect. Whether the cache is warm or cold isn't so relevent; more's to
the point, the savings show best on the second and subsequent accesses
when the data to be read *is* cached and therefore there's no disk
traffic at all.