Date: Sat, 21 Aug 1999 15:42:20 +0200 From: Christian Weisgerber <naddy@mips.rhein-neckar.de> To: mjacob@feral.com Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: Bizarre effect reading old tape Message-ID: <19990821154220.H16148@mips.rhein-neckar.de> In-Reply-To: <Pine.BSF.4.05.9908201630110.83055-100000@semuta.feral.com>; from Matthew Jacob on Fri, Aug 20, 1999 at 04:30:49PM -0700 References: <7pkc9u$btm$1@bigeye.rhein-neckar.de> <Pine.BSF.4.05.9908201630110.83055-100000@semuta.feral.com>
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Matthew Jacob: > You didn't say what drive you are reading it on. My guess is that if > you're reading this on a 51000 that it is adding in the nulls, but I could > be wrong. Yes, I'm reading it on the 51000. I'm fairly sure that I've previously read that tape on the 51000 under Linux *without* inserted null blocks, so I think it can't be the drive alone. If I always got 512-byte chunks of data and nulls, that would be more plausible. But I always get contiguous data for half the read size. "dd bs=10k" does 10,240-byte reads. "mt stat" confirms that the driver is in 1024-byte fixed blocksize mode. According to sa(4), this should mean that each 10,240-byte read() is converted into a series of ten 1024-byte block reads. So why do I end up with 5,120 bytes of straight data followed bt 5,120 bytes of straight nulls? -- Christian "naddy" Weisgerber naddy@mips.rhein-neckar.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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