> From: Chris Thompson [mailto:cet1@cus.cam.ac.uk]
>
> Ethan Torretta <ejt(a)tellme.com> writes:
> > "Michael J. Tuciarone" <tooch(a)netapp.com> wrote:
> > > As filers have received more main memory, we began running out of
> > > reserved disk areas before the whole core was dumped. The actual
> > > ratio of memory to disk depends on memory size and disk model;
> > > the larger the ratio the more likely you'll be unable to dump the
> > > whole core. In response, we implemented the compressed
> core feature.
> > > Now if the filer computes there isn't enough disk space
> to save the
> > > entire core uncompressed, we compress the core before
> writing it out.
> >
> > This makes me very interested in providing enough disks to allow
> > uncompressed cores. However, looking at the documentation
> I don't think
> > that's going to happen. According to the SAG, each disks
> provides only
> > 20 MB of dump space, so for an F760 with 1024 MB of main
> memory, fifty-two
> > disks will be necessary for an uncompressed dump. Is this
> correct?
> > The chart still says only fourteen for "256 or more." I've
> got fourteen
> > on each filer; if twenty, say, would do it, I'd rearrange
> filers so that
> > the most sensitive ones had twenty, but fifty-two is out of
> the question.
>
> The problem would seem to be that the 20 MB reserved area
> hasn't altered
> from the days of 2 GB, maybe 1 GB, discs, and so things have
> got out of
> proportion.
>
> How about using the space wasted by "right-sizing" for dumps?
> Only if it
> exists, of course, but in practice it will, and will be a lot
> more than
> 20 MB per disc!
>
As you said above, the 20MB reserved area is the same on all
sized disks. However we do use the space that is left over after
right-sizing. The size of the space varies with the capacity
of the disk.
In a coming release compression of the core will be deferred
if there is enough space available on the disk. In addition
the core will be sprayed to multiple disks in parallel (it
currently is written synchronously to one disk at a time).
This is for fibre channel disks only.
-steve