Date: Tue, 26 May 1998 20:34:42 -0400 (EDT) From: Simon Shapiro <shimon@simon-shapiro.org> To: "Kenneth D. Merry" <ken@plutotech.com> Cc: owensc@enc.edu, tom@sdf.com, freebsd-stable@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG, rzig@verio.net Subject: Re: DPT install problem Message-ID: <XFMail.980526203442.shimon@simon-shapiro.org> In-Reply-To: <199805262137.PAA00792@panzer.plutotech.com>
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On 26-May-98 Kenneth D. Merry wrote:
> Simon Shapiro wrote...
>> On 22-May-98 Raul Zighelboim wrote:
>> > As a sidebar; the DOS configuration software can only create arrays
>> > with
>> > up to 1 mbyte interleave. Is this a limitation on the hardware or the
>> > software ? Is (will there be) a way to create an array with a larger
>> > interleave (32 megs comes to mind).
>>
>> An interleave factor larger than 1MB will be very inefficient:
>>
>> a. The SCSI bus will be used (locked) for long periods. This will
>> cause poor multi-tasking response.
>>
>> b. The cache memory will be able to contain very few stripes.
>>
>> Also notice that in the context of FreeBSD, anything larger than 64K is
>> sort of mute, as the O/S limits all SCSI transfers to that size. I do
>> not
>> know yet how CAM will do, but suspect it to be the same.
>
> It will be the same. The 64K limitation is a generic FreeBSD
> limitation, so CAM won't change it. CAM won't limit it, though. Here at
> Pluto, we've been running large chunks (> 64K) through CAM and the
> Adaptec
> driver by passing physical memory addresses in through the passthrough
> driver. (and therefore you bypass the whole struct buf thing and physio)
Ugly :-) We need this type of support in raw devices, though, so userland
can pass it in reasonable manner.
> If we ever get a buffer chaining (or similar) scheme in place,
> it'll be possible to do any size I/O without jumping through hoops.
>
>> > Thanks, Simon, for a job well done.
>>
>> Thanx. I am going to get started on CAM port in the next few days.
>
> Good deal. Contact me via private email about getting access to
> the CAM source repository.
>
> Ken
> --
> Kenneth Merry
> ken@plutotech.com
---
Sincerely Yours,
Simon Shapiro Shimon@Simon-Shapiro.ORG
770.265.7340
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