BIOS booting from disks > 2TB
José María Alcaide
jose at we.lc.ehu.es
Thu Nov 20 09:39:11 UTC 2014
> El 20/11/2014, a las 9:15, James R. Van Artsdalen <james-freebsd-fs2 at jrv.org> escribió:
> The extended BIOS disk functions, introduced onto PCs almost 20 years ago, allowing for addressing LBAs beyond 2TB. FreeBSD will use these BIOS functions when present. This is usually not a problem.
> If a disk controller card of some kind is installed then the option ROM on that card must support the extended BIOS disk functions for this to work. This is usually not a problem.
> The error messages shown only pertained to the backup header, not primary, and looking at the code it implies to me that the primary header and table were read OK, and that these will be used even if the backup cannot be found. I think "invalid backup GPT header" is a warning in this case, not a fatal error.
> I think the real problem is here:
> Can't work out which disk we are booting from.
> Guessed BIOS device 0xffffffff not found by probes, defaulting to disk0:
> 1. If you replace the 3TB disk with a disk 2TB or smaller and make no other change, does this error still happen?
> 2. How are the disks connected to the system? What disk controllers are used? What is the system BIOS boot disk setting set to?
I have an identical system (Proliant Microserver Gen8) with same hardware configuration, same firmware versions and same disks (WD Red 3 TB) as Borja's system.
When the disk controller is configured in AHCI mode there is no way of selecting the boot disk (among those connected to the disk controller). The BIOS only permits to select the boot disk controller, if there is more than one (which is not the case). So I think that the message
Can't work out which disk we are booting from.
Guessed BIOS device 0xffffffff not found by probes, defaulting to disk0:
is harmless (given that we actually want to boot from the first disk).
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.
Jose M. Alcaide
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