Filesystem question

Christopher R. Hertel crh at
Thu Oct 12 21:32:48 GMT 2000

> > OS vendors do work on this (I'm happy to say I benchmarked a Solaris 8
> > improvement in this very area this spring), but some things are
> > appropriate to cache in applications which know the usage pattern of
> > their users.
> Perhaps; I'm still not convinced... if Solaris is already caching the data
> in question,

But that's the point.  Samba has caches for mangled names--something that
Solaris won't know or care about.  Other things to cache are any case
conversions, reformatting of directory or file information, etc.  That is,
anything that Samba has to massage before handing it across the wire.  One
suggestion was that Samba might cache icon images because Windows Explorer
digs within files and directories every time you wave the mouse across an
Explorer window.  Even with an OS cache, you're likely to generate cache 
misses for application-specific data.

> surely a Samba-side cache will only cut out whatever
> overheads Solaris has on cache hits? Also, why isn't the client caching
> this data - ISTR Windows 9x/NT does have a client-side cache for networks,
> so what's going wrong??

Depends on what data the client does cache.  I think we're talking about 
empirical data here.  Users are reporting disk overhead.

> > Some careful groveling over the requests sent by Windows Explorer may
> > well point to places where both we and Microsoft can improve things.
> Undoubtedly; if you go prodding the innards of NT, you'll see some
> HORRIBLE things. At one point, Explorer needs to calculate the length of a
> string - which it does by sending a 0 and the string over RPC, and
> receives a 1 and the string minus one character. Repeat until the string
> is empty...

Well... ick.

Anyway, the key for Samba is to take a look at the empirical information
and see what can be tweaked.

Also, some of this discussion was started by folks trying to port Samba to
non-posixy platforms where the OS cache isn't as big.  Their idea was to
build a VFS module custom to their platform.  Thus, it wouldn't impact
Samba per. se.  It would be a fix for their own OS. 

Chris -)-----

Christopher R. Hertel -)-----                   University of Minnesota
crh at              Networking and Telecommunications Services

    Ideals are like stars; you will not succeed in touching them
    with your choose them as your guides, and following
    them you will reach your destiny.  --Carl Schultz

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