Path: utzoo!attcan!uunet!ginosko!uakari.primate.wisc.edu!ames!pacbell!indetech!fiver!palowoda From: palowoda@fiver.UUCP (Bob Palowoda) Newsgroups: comp.unix.i386 Subject: Re: Mylex SCSI Controller Message-ID: <831@fiver.UUCP> Date: 30 Sep 89 10:12:54 GMT References: <372@csense.UUCP> Organization: Fiver Communications Fremont, Ca Lines: 54 From article <372@csense.UUCP>, by bote@csense.UUCP (John Boteler): > From article <19245@gatech.edu>, by ken@gatech.edu (Ken Seefried III): >> In article <369@csense.UUCP> bote@csense.UUCP (John Boteler) writes: >>>Curious as to how a SCSI host controller can easily perform >>>cache operations? >> the DPT controller for some excellent commentary, pro and con, on >> the issues involved in caching disk controllers... > > I don't need to. > > I talked to one of the engineers from DPT at Comdex. He explained > to me the difficulty of caching a SCSI host controller: since > the controller handles up to seven devices on the SCSI bus, > putting the cache system on the controller makes for little > improvement, if any. Did DPT do a display a real comparison of throughput at Comdex? Does DPT manufacture a SCSI cacheing controller? The only reason I mention this is if I where at Comdex showing off my ESDI controller. I surely would build your confidence in the product. But I don't think it a fare comparison between these two types of controllers. A better comparison of the DPT would be to that of Adaptec's new ESDI cacheing controller. > The best solution, and one which has > been implemented by at least one drive manufacturer, is to > put the caching components on the SCSI drive. I thought SCSI drives have buffers? > > When a SCSI request is sent to the drive by the controller, the > controller is free to service one of the other six devices on > the bus and the drive can check its own cache for the presence > of the data requested and respond accordingly. Won't the Mylex controller service the request from the cache? Another thing about the Mylex controller, it is 32 bit. DPT is 16 bit I believe. Something else I don't quite understand is how they sync it with the cpu cycle. ---Bob -- Bob Palowoda packbell!indetech!palowoda *Home of Fiver BBS* login: bbs Home {sun|dasiy}!ys2!fiver!palowoda (415)-623-8809 1200/2400 Work {sun|pyramid|decwrl}!megatest!palowoda (415)-623-8806 2400/9600/19200 TB Voice: (415)-623-7495 Public access UNIX XBBS