From owner-freebsd-current Tue Dec 24 16:44:18 1996 Return-Path: Received: (from root@localhost) by freefall.freebsd.org (8.8.4/8.8.4) id QAA17823 for current-outgoing; Tue, 24 Dec 1996 16:44:18 -0800 (PST) Received: from Octopussy.MI.Uni-Koeln.DE (Octopussy.MI.Uni-Koeln.DE [134.95.166.20]) by freefall.freebsd.org (8.8.4/8.8.4) with SMTP id QAA17809 for ; Tue, 24 Dec 1996 16:44:09 -0800 (PST) Received: from x14.mi.uni-koeln.de (annexr3-18.slip.Uni-Koeln.DE) by Octopussy.MI.Uni-Koeln.DE with SMTP id AA24399 (5.67b/IDA-1.5 for ); Wed, 25 Dec 1996 01:44:04 +0100 Received: (from se@localhost) by x14.mi.uni-koeln.de (8.8.4/8.6.9) id BAA01001; Wed, 25 Dec 1996 01:44:02 +0100 (CET) Message-Id: Date: Wed, 25 Dec 1996 01:44:01 +0100 From: se@freebsd.org (Stefan Esser) To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch) Cc: freebsd-current@freebsd.org (FreeBSD-current users), cg@archimedia.khs-linz.ac.at Subject: Re: DAT: reading with blocksize=256K References: <199612240747.IAA10234@uriah.heep.sax.de> X-Mailer: Mutt 0.54-PL15 Mime-Version: 1.0 In-Reply-To: <199612240747.IAA10234@uriah.heep.sax.de>; from J Wunsch on Dec 24, 1996 08:47:35 +0100 Sender: owner-current@freebsd.org X-Loop: FreeBSD.org Precedence: bulk On Dec 24, j@uriah.heep.sax.de (J Wunsch) wrote: > As Christian Gusenbauer wrote: > > > I just got a DAT cartridge with a tar backup. It seems that the backup > > was made with a blocksize of 256K. Isn't it possible to get the data into > > my pc with current (it looks like there's a limit of 64K)?? > > This has been discussed at lenth already: it's currently limited by > physio(9) to chunks of at most 64 KB size, due to the limitations in > the scatter/gather list of some SCSI controllers that don't allow for > more than 16 scatter/gather segments. I can't talk for any other driver, but in case of the NCR driver, a simple rebuild of the kernel with MAX_SCATTER (in /sys/pci/ncr.c) set to 129 will allow to read 256KB tape blocks. (I guess the same is true for most other SCSI host adapters, that don't have a lower adapter firmware limit.) The drivers may be sub-optimal for typical (shorter) transfers, then, but if you just need to read THAT tape ... Regards, STefan