Date: Wed, 2 Jun 2004 07:11:53 -0600 From: "Kenneth D. Merry" <ken@kdm.org> To: David Malone <dwmalone@maths.tcd.ie> Cc: freebsd-scsi@freebsd.org Subject: Re: 1TB issue Message-ID: <20040602131153.GA77049@panzer.kdm.org> In-Reply-To: <20040602094939.GA48588@walton.maths.tcd.ie> References: <200406012304.i51N4pV4013286@himinbjorg.tucs-beachin-obx-house.com> <20040601234010.GA72828@panzer.kdm.org> <20040602094939.GA48588@walton.maths.tcd.ie>
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On Wed, Jun 02, 2004 at 10:49:39 +0100, David Malone wrote: > On Tue, Jun 01, 2004 at 05:40:10PM -0600, Kenneth D. Merry wrote: > > See another recent message on this list from Brooks Davis. It sounds like > > sysinstall has issues with large arrays in -current, but fdisk works okay. > > I've heard from some people that there was a 2TB limit on SCSI > devices, but it wasn't clear to me if this was a limit of the SCSI > implementation they were using, or if it arose from the SCSI spec. > What's actually the case here? It's a limitation in the device they're using and/or the SCSI layer they're using. With 10 or 12 byte read/write CDBs, you're limited to 32 bits to specify the LBA. For a device with 512 byte sectors, that limits you to 2TB. With the SBC-2 spec, they (T10) introduced 16 byte read, write and read capacity commands. That allows you to get the size of a device larger than 2TB, and address blocks past the 2TB limit. (The size of the LBA field was increased to 8 bytes for the 16 byte commands, so you can address 2^64 blocks.) CAM in FreeBSD-current has had support for devices larger than 2TB for a little over a year. -stable doesn't have that support, because it has other limitations (pointed out by Bruce) that basically mean CAM support for large devices wouldn't really matter. Ken -- Kenneth Merry ken@kdm.org
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