[OpenAFS] Very large caches

[Nathan Neulinger]

I've got a 15GB cache on our web server, and a 10GB one on our ftp
mirror server, both work pretty well, except they take quite a while to
scan at boot, even with the cache-subdir support. I haven't messed with
changing the chunk size, but I'd presume that would cut the time down
significantly, albeit at the expense of # of distinct files in the
cache. (I really need to get back to one of my to-do-list items about
reworking the dumpcache tools to build clean w/ openafs as well as
possibly merging them into fs.)

There is definately something nice about holding your entire web site
inside the cache. Definately appears to boost performance, especially
when you have local web indexing that would repeatedly flush out the
entire cache if it were small (300MB). I won't deploy any machine with
less than a 250MB cache if I can help it.

-- Nathan

Derek Atkins wrote:
> 
> I was never running with a cache that big.  I was running
> a 3GB cache and it worked ok.  I never filled it nor did
> I actually run any performance tests.
> 
> Recent versions of OpenAFS should support it relatively well.
> 
> -derek
> 
> Nickolai Zeldovich <kolya@MIT.EDU> writes:
> 
> > > ...  is it useful to have a, say, 18Gb client cache?
> >
> > You might hit some performance problems in the dcache code with a
> > cache that large.  There's a number of places where the dcache code
> > does linear scans of all dcache entries, and you'll potentially have
> > 1.8 million dcache entries in the kernel.  (You could probably cut
> > that down to ~280k by having fewer dcache entries and assuming you'll
> > cache mostly whole 64K chunks, but it's still quite a bit.)
> >
> > It'd be interesting to see what particular performance problems you
> > would infact hit with such a large cache, and fix them, but that's
> > more in the long run..
> >
> > -- kolya
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> 
> --
>        Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
>        Member, MIT Student Information Processing Board  (SIPB)
>        URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
>        warlord@MIT.EDU                        PGP key available
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-- 


------------------------------------------------------------
Nathan Neulinger                       EMail:  nneul@umr.edu
University of Missouri - Rolla         Phone: (573) 341-4841
Computing Services                       Fax: (573) 341-4216