Date: Sat, 26 Aug 2006 22:11:10 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Scott Long <scottl@samsco.org> Cc: Dave Kingsley <david.kingsley@enc.edu>, Julian Elischer <julian@elischer.org>, freebsd-hardware@freebsd.org Subject: Re: sysinstall disklabel limit Message-ID: <20060826214758.N73381@delplex.bde.org> In-Reply-To: <44EF43A6.1050003@samsco.org> References: <44EEE36E.1040201@enc.edu> <200608251353.20035.jhb@freebsd.org> <44EF43A6.1050003@samsco.org>
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On Fri, 25 Aug 2006, Scott Long wrote: > John Baldwin wrote: >> I think there are some patches to fix sysinstall, but it still tops out at >> 2TB I thought. cc'ing some folks who probably know better than I. > > Simply put, neither the fdisk nor the bsd partition schemes can address more > than 2TB of storage. This is inherent limitations to the formats. > Users who run into this are encouraged to either use a GPT for partitioning, > or simply put the filesystem onto the storage without any > partitioning. Too simply to be correct. They are limited to 2^32 logical sectors. If the logical sector size is 512, this gives the 2TB limit. Logical sector sizes different from physical sector sizes are easy to configure for the disk label partition scheme (the logical sector size is whatever is in the label), but this might be broken in -current. Logical sector sizes different from physical sector sizes are not so easy to configure in the MBR since there is nowhere in the MBR to specify the sector size and the MBR may be used for booting or shared with other operating systems. Most file systems have a preferred block size of 2K or 4K, so useful granularity would rarely be lost by using a physical sector size of 2K or 4K, but physical sector sizes are still normally 512 for compatibility (except for devices that haven't existed for more than 20 years, like cdroms). With a physical or logical block size of 4K, the practical limit from the MBR and disk label schemes is 16TB. Bruce
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