Date: Thu, 20 Nov 2014 10:50:24 +0100 From: Borja Marcos <borjam@sarenet.es> To: =?iso-8859-1?Q?Jos=E9_Mar=EDa_Alcaide?= <jose@we.lc.ehu.es> Cc: freebsd-fs@freebsd.org Subject: Re: BIOS booting from disks > 2TB Message-ID: <7CAD9C0C-E793-4DA8-8ED0-AAB01C77F52C@sarenet.es> In-Reply-To: <D91EAD51-2B6B-41E6-891E-575153409745@we.lc.ehu.es> References: <17A2AC72-AD70-480A-9BAC-9CC8EAFD572F@we.lc.ehu.es> <alpine.BSF.2.11.1411191024540.55133@wonkity.com> <FF60956B-BF1F-4A1A-840E-489C549304EF@sarenet.es> <546DA321.8050403@jrv.org> <D91EAD51-2B6B-41E6-891E-575153409745@we.lc.ehu.es>
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On Nov 20, 2014, at 10:38 AM, Jos=E9 Mar=EDa Alcaide wrote: > Can't work out which disk we are booting from. > Guessed BIOS device 0xffffffff not found by probes, defaulting to = disk0: >=20 > is harmless (given that we actually want to boot from the first disk). >=20 > In fact I did another test: I installed FreeBSD on an 8 GB partition = *using the MBR scheme instead of GPT*, and the system booted from the = first 3 TB disk without any problem (and with four disks attached), = despite of showing the same warning message. So, that 0xffffffff might be a buffer overflow being triggered by a = failed attempt to read the backup GPT table? Let's assume that the BIOS is poorly implemented and it won't read = beyond the 2 TB limit. As far as I know, booting from a MBR disk doesn't require reading = anything but the "classic" partition table and the partition we are using. So, as long as the partition fits inside that 2 TB limit it = should work, and it does. Booting from GPT, however, requires reading the end of the disk. Or is = the backup copy of the partition table read if and only if there's some problem with the main one?=20 Can BIOS be reporting a wrong size for the disk (after all we are = assuming a dodgy BIOS) and making gptboot to cosider the table corrupt, hence causing it to try to read the backup copy? Whatever, that 0xffffffff parameter (which should be something like = 0x80) looks like a corrupted variable to me, which would mean we have some buffer overflow? Maybe I'll try to recompile the boot chain removing the backup reading = and the sanity checks and see what happens. Borja.
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