Re: file system and raid performance

On Thu, Aug 7, 2008 at 3:08 PM, Mark Mielke <mark(at)mark(dot)mielke(dot)cc> wrote:
> Andrej Ricnik-Bay wrote:
>
> 2008/8/8 Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>:
>
>
> noatime turns off the atime write behaviour. Or did you already know
> that and I missed some weird post where noatime somehow managed to
> slow down performance?
>
>
> Scott, I'm quite aware of what noatime does ... you didn't miss a post, but
> if you look at Mark's graphs on
> http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide
> they pretty much all indicate that (unless I completely misinterpret the
> meaning and purpose of the labels), independent of the file-system,
> using noatime slows read/writes down (on average)
>
> That doesn't make sense - if noatime slows things down, then the analysis is
> probably wrong.
>
> Now, modern Linux distributions default to "relatime" - which will only
> update access time if the access time is currently less than the update time
> or something like this. The effect is that modern Linux distributions do not
> benefit from "noatime" as much as they have in the past. In this case,
> "noatime" vs default would probably be measuring % noise.

It appears that the default mount option on this system is "atime".
Not specifying any options, "relatime" or "noatime", results in
neither being shown in /proc/mounts. I'm assuming if the default
behavior was to use "relatime" that it would be shown in /proc/mounts.

Regards,
Mark