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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.ecn.uoknor.edu!news.wildstar.net!imci5!pull-feed.internetmci.com!newsfeed.internetmci.com!feed1.news.erols.com!howland.erols.net!www.nntp.primenet.com!nntp.primenet.com!news.mathworks.com!fu-berlin.de!irz401!orion.sax.de!uriah.heep!news From: j@uriah.heep.sax.de (J Wunsch) Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: SCSI tape block size Date: 6 Oct 1996 18:09:29 GMT Organization: Private BSD site, Dresden Lines: 33 Message-ID: <538skp$90e@uriah.heep.sax.de> References: <8720ffxq0j.fsf@plm.xs4all.nl> <536grc$ba@uriah.heep.sax.de> <537u8o$b8@mscu.snafu.de> Reply-To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch) NNTP-Posting-Host: localhost.heep.sax.de Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Newsreader: knews 0.9.6 X-Phone: +49-351-2012 669 X-PGP-Fingerprint: DC 47 E6 E4 FF A6 E9 8F 93 21 E0 7D F9 12 D6 4E matthias@mscu.snafu.de (Matthias Schuendehuette) wrote: > > (Note that 64 KB is the largest blocksize currently supported inside > > the kernel by physio(), so there's no use in making the parameter > > above larger.) > > There was a rather large thread in de.comp.os.unix on reading > tar-archives from SGI machines which have default blocksizes of 256 KB. I've read it (and posted there -- as you probably know). And yes, FreeBSD currently cannot read these tapes, that's where we've got aware of the problem at all. > 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... -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)