Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!zds-ux!gerry
From: gerry@zds-ux.UUCP (Gerry Gleason)
Newsgroups: comp.periphs.scsi
Subject: Re: Controller Cache vs. Software Cache
Message-ID: <633@zds-ux.UUCP>
Date: 12 Jun 91 17:21:01 GMT
References: <30738@hydra.gatech.EDU>
Reply-To: gerry@zds-ux.UUCP (Gerry Gleason)
Distribution: comp.periphs.scsi
Organization: Zenith Data Systems
Lines: 22

In article <30738@hydra.gatech.EDU> jt34@prism.gatech.EDU (THOMPSON,JOHN C) writes:
>How does the performance of a scsi host adaptor with built in caching hardware
>compare to the performance of a software caching program or OS caching?
>Which is faster? Is onboard drive caching even faster? Any definitive research
>on this subject? Is there a source on the net for a scsi perpiheral benchmark
>program/source code? Thanks

Logically, software caching must be faster (assuming reasonalble
implementations in both cases), in the case of a cache hit because it
can just hand over the data rather than needing to perform an I/O
operation.  On the other hand, there is one type of hardware caching
that does make sense, read-ahead track buffering, but even this can
be handled to some extent in software, and it's better done in the
drive itself if your going to do it at all (and some drives do).

Now, this doesn't mean there aren't other reasons for wanting a cache
on the controller; for example, so you can implement special multi-drive
features such as mirroring, arrays, etc.  If the controller designer
does it right, they could introduce a simple caching controller and
later provide these advanced features as a firmware upgrade.

Gerry Gleason