Date: Wed, 30 Sep 1998 12:58:58 -0500 From: Karl Denninger <karl@Denninger.Net> To: "Justin T. Gibbs" <gibbs@narnia.plutotech.com> Cc: scsi@FreeBSD.ORG Subject: Re: Long IDE probes? Message-ID: <19980930125858.B4304@Denninger.Net> In-Reply-To: <199809301749.LAA24440@narnia.plutotech.com>; from Justin T. Gibbs on Wed, Sep 30, 1998 at 11:49:12AM -0600 References: <199809301749.LAA24440@narnia.plutotech.com>
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On Wed, Sep 30, 1998 at 11:49:12AM -0600, Justin T. Gibbs wrote: > > SCSI devices similarly are probed by the adapter BIOS. Again, there is no > > reason for the long wait that I can fathom. > > Then you don't fathom SCSI. When the system comes up, it resets the > SCSI bus to ensure that all previously negotiated transfer negotiations > have been nullified. Some devices take longer than others to respond > after a bus reset. If you are dealing with modern disks, you only need > to wait ~100ms. If you are dealing with tape drives, some cdrom drives, > or older devices, you must wait longer or risk "not seeing" the device. > The bus settle delay is easily configurable so that people with nice > devices can shorten it, but the default delay in GENERIC is there for > a very good reason. > > -- > Justin The default was recently increased (read: made longer) - like doubled. I *KNOW* that things like Exabytes "go away" for short periods of time after a bus reset. But we're talking about *defaults* here, and modern disks and tape drives, while they may kvetch internally for a while before they'll generally be useful, but virtually all will respond to an inquiry within 3-5 seconds - maximum. -- -- Karl Denninger (karl@denninger.net) http://www.mcs.net/~karl I ain't even *authorized* to speak for anyone other than myself, so give up now on trying to associate my words with any particular organization. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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