mfs and buildworlds on the SunFire x4600

[Mars G. Miro]

On 5/8/07, Oliver Fromme <olli at lurza.secnetix.de> wrote:
> Mars G. Miro wrote:
>  > Oliver Fromme wrote:
>  > > By the way, what are you actually trying to do?  What is
>  > > your goal?  Do you need to reduce the buildworld time?
>  >
>  > as i've mentioned in my original email, does mfs speed up I/O stuff ?
>
> Sometimes it does.  But most of the time, a real disk
> partition with soft-updates on it is just as fast.
> With soft-updates, writing is asynchronous, i.e. it
> goes to RAM first, just like a memory disk.  The data
> is later committed to disk in the background, so the
> processes don't have to wait for it.  And once the
> data is in the cache, reading is just as fast (or even
> faster) as a memory disk.  Note that /usr/src will
> fit in the cache easily if you have several GB of RAM.
>
> I usually have a memory disk as /tmp, but that's really
> just for historical reasons.  And it's easier to clean
> up -- just umount it.  ;-)
>
>  > there's been a lot of threads in teh past that a buildworld on mfs
>  > increases speed --- tho it might not be the appropriate test for
>  > high-end machines (speaking of w/c I just gots a T2000).
>
> It depends on what exactly you want to test, and for
> what reason.  You probably have already wasted much
> more time with your experiments and testing than you
> can ever save by using mfs for buildworld.
>

wasted my time? dont think so.

now we know buildworld on mfs dont really matter on high-end machines,
and it didnt even then when i tried it on my single-proc Opteron w/ 1G
of RAM almost 2 years ago on 5.X (i recall having to crash when i used
malloc but then this is documented)

and I'd think testing it on something like my x4100 w/ 8G of RAM may
produce the same results..

so teh conclusion would be, buildworld isnt teh appropriate test if
mfs does really speed things up, other apps/tools may be much more
appropriate --- that or, does mfs speeding things up really work?
remains to be seen ...

>  > there's prolly other appropriate apps/tools for mfs-testing ...
>
> I don't think it makes much sense to benchmark mfs.
> It is a known fact that a real tmpfs (like Solaris and
> Linux have) would be better.  I think it's even listed
> on the FreeBSD ideas web page, but nobody is actively
> working on it, AFAIK.  On the other hand, I'm not 100%
> convinced that it would be worth the effort either.
>

it does to me, however, and perhaps other people too ;-)

> It would be interesting to see how ZFS on a swap-backed
> vnode device would perform on FreeBSD 7-current (with
> and without compression).
>
> Best regards
>    Oliver
>
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cheers
mars