[coreboot] 2 Terabyte Limit of BIOS/MBR

Martin Marcher martin at marcher.name
Sat Jan 12 20:20:13 CET 2008

On Thursday 10 January 2008 22:55 Carl-Daniel Hailfinger wrote:

> On 10.01.2008 21:59, Martin Marcher wrote:
>> Hello,
>> hope to be in the right place to ask this, if not just point me to where
>> you think it's apropriate
>> my Hardware is:
>> Tyan Transport GT20 (B2865)
>> http://www.tyan.com/support_download_manuals.aspx?model=B.GT20B2865
>> an Areca 1210 raid controller is attached to it and I just was hit by the
>> 2TB limit which a BIOS can handle.
> Is the RAID array exactly 2 TB? Then the BIOS will see its size as 0.

nope it's 3TB total. Running debian/etch

we have seperate /boot / partitions and most of the space is used by some
xen domUs. / is inside an LVM (guess that doesn't matter a lot since debian
itself is ready for the large block device support)

> Why should we replicate such a bug? If you use Linux as bootloader
> inside LinuxBIOS and if the Linux kernel has support for devices >2 TB
> enabled (all recent kernels do), you can boot from disks up to 65535 TB
> (maybe even 131071 TB) if the adapter creates a virtual SATA device (the
> limits are what you would expect from LBA48 addressing). Depending on
> the device driver (you said the RAID adapter claims to be SCSI), the
> limit may be even higher.

the problem is I don't get to boot linux. Tried to boot from a cd with only
grub on it but after some reading I concluded that grub relies on the disks
reported from the bios. All grub finds is (cd) and fd0-9 - not a single hd

> Three "solutions":
> 1. Use LinuxBIOS and Linux as Bootloader (LAB)
> 2. Use the vendor BIOS and boot from a smaller disk

I do that right now, but I consider it a not optimal solution

> 3. Use the vendor BIOS, but make sure the RAID is either smaller than 2
> TB or a few GB bigger than 2 TB (in that case the detected size would
> probably be real size minus 2 TB). To be honest, this tip may or may not
> work, depending on how broken the BIOS is.

well it's not working since the disk is "stuck" at >2TB (750GB are used the
rest is free, but the raid controller doesn't have an option to shrink it

>> 3) Last, not least I couldn't the Tyan GT20 in the supported hardware
>> list, is that true or just missing.
> True. It should be supportable, though, if we have one board to
> experiment with. The Tyan Tomcat K8E S2865 is the board inside according
> to the manual.
>> If it's missing I'll bug Tyan about this once a month or so, in case you
>> don't have the specs available to send it to you (if you want me to do
>> that).
> How much time are you willing to invest to port LinuxBIOS to the board?

If it was only me: as much as needed

We are a small company with 2 physical server but given I could find a setup
where I can install and uninstall linuxbios securely (in case it won't
work) I guess I could talk my boss into allowing me to regularly taking the
server down and test the bios - reading up on this in the wiki now



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