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From: matthias@mscu.snafu.de (Matthias Schuendehuette)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: SCSI tape block size
Date: 9 Oct 1996 14:29:35 GMT
Organization: private UUCP-site running FreeBSD 2.1.5.R
Lines: 27
Message-ID: <53gcsf$7q@mscu.snafu.de>
References: <8720ffxq0j.fsf@plm.xs4all.nl> <536grc$ba@uriah.heep.sax.de>
<537u8o$b8@mscu.snafu.de> <538skp$90e@uriah.heep.sax.de>
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In article <538skp$90e@uriah.heep.sax.de>,
> matthias@mscu.snafu.de (Matthias Schuendehuette) wrote:
> [...]
>> Not to acknowledge this nonstandard behaviour of IRIX but would it be a
>> great effort to extend the max. blocksize in physio() and what would be
>> the drawbacks of doing so?
>
> The limitation arises out of the simple fact that quite some SCSI host
> adapters do not support more than 16 scatter/gather segments. In an
> VM architecture, you need one scatter/gather segment per logical page
> in the worst case. This makes 16 * 4 KB = 64 KB. Relinguishing this
> limit would require a partial rewrite of some of the lower-level
> drivers (they probably have to use bounce buffers or something like
> that).
>
> Despite of this, i still think SGI is plain insane in this...
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Thanks J"org, that was all I wanted to know :-)))))
Ciao/BSD - Matthias
--
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