[LinuxBIOS] 2 Terabyte Limit of BIOS/MBR

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Thu Jan 10 22:55:07 CET 2008

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.

> Is that right that the problem is the BIOS?


> how I understand the different articles at wikipedia, ms and different
> netsources the BIOS just can't handle disks that are larger than 2TB, in
> turn this renders a MBR unusable. Fine so I convert the disk to a GPT and
> off I should go. But I found that the bios of this board still refuses to
> accept the disk (reported as an scsi device from the controller) and just
> says "No BIOS disk found".

Haha. Nice bug.

> OK, now the actual question(s):
> 1) Is this problem (if I understood it right) still there with linuxbios?

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.

> 2) If so what plans are there to still be able to use a >2TB disk?
> (Note: Just plugging a smaller disk to boot from isn't exactly what I
> consider a solution, however you are the experts :)

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

> 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?


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