From owner-freebsd-scsi Mon Aug 4 23:55:54 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.5/8.8.5) id XAA24880 for freebsd-scsi-outgoing; Mon, 4 Aug 1997 23:55:54 -0700 (PDT) Received: from sax.sax.de (sax.sax.de [193.175.26.33]) by hub.freebsd.org (8.8.5/8.8.5) with SMTP id XAA24875 for ; Mon, 4 Aug 1997 23:55:50 -0700 (PDT) Received: (from uucp@localhost) by sax.sax.de (8.6.12/8.6.12-s1) with UUCP id IAA27169; Tue, 5 Aug 1997 08:55:49 +0200 Received: (from j@localhost) by uriah.heep.sax.de (8.8.5/8.8.5) id IAA15949; Tue, 5 Aug 1997 08:35:04 +0200 (MET DST) Message-ID: <19970805083504.NT06658@uriah.heep.sax.de> Date: Tue, 5 Aug 1997 08:35:04 +0200 From: j@uriah.heep.sax.de (J Wunsch) To: scsi@FreeBSD.ORG Cc: dkelly@hiwaay.net Subject: Re: Maximum Tape Block Size? References: <199708042257.RAA12906@nexgen.hiwaay.net> X-Mailer: Mutt 0.60_p2-3,5,8-9 Mime-Version: 1.0 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 Reply-To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch) In-Reply-To: <199708042257.RAA12906@nexgen.hiwaay.net>; from dkelly@hiwaay.net on Aug 4, 1997 17:57:39 -0500 Sender: owner-freebsd-scsi@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk As dkelly@hiwaay.net wrote: > A year or so ago I recall Jordan had an SGI DAT tape with 256k blocksize > which wouldn't read on FreeBSD. Am wondering how this problem was > eventually solved? No, it hasn't. The problem is the way requests are being `sliced' in physio(9). Right now, physio() uses a fixed 64 KB slicing, which is the smallest common denominator for the SCSI controller with the smallest scatter-gather list (AHA1540 with 16 segments per 4 KB in worst case, one page each). At least, that's how i understood it. It should be made more flexible so that controllers with larger scatter-gather lists could be handled efficiently. Those with a small list could perhaps optionally use a large physically contiguous region as a bounce buffer, but that's quite wasteful. Feel free to implement a better scheme. ;-) -- 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. ;-)