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 Message-ID: <Mutt.19961225014401.se@x14.mi.uni-koeln.de> In-Reply-To: <199612240747.IAA10234@uriah.heep.sax.de>; from J Wunsch on Dec 24, 1996 08:47:35 %2B0100 References: <Pine.BSF.3.91.961224002318.181A-100000@spock.my.domain> <199612240747.IAA10234@uriah.heep.sax.de>
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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
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