Re: Grub rescue

[Chris Murphy]

On Mar 24, 2013, at 4:19 PM, David WE Roberts <address@hidden> wrote:

> The hardware in question has EFI capability but is running at the moment 
> in legacy mode.

That sucks. Almost invariably that means no native AHCI-SATA support due to the 
typical CSM implementation limiting what the hardware can do. You'll probably 
get IDE like speeds from disks, almost disqualifying for SSD usage, or RAID, 
and maybe it even affects the performance of a single recent HDD as those 
speeds are now regularly above 150MB/s even for laptop drives. So I'd 
re-evaluate this. The CSM-BIOS is desperation, for running things like Windows 
XP. It's not for running a reasonably recent linux distribution.

> However the primary MBR SSD has really only space for one operating 
> system, which is Windows 7, so I need to be able to boot my luxuries off 
> the GPT disc.

Windows 7 only boots from MBR disks on BIOS hardware. Windows 7 only boots from 
GPT disks on UEFI hardware.

Realize you're limiting the performance of that SSD by running the firmware in 
legacy mode.

> 
> However I don't want at the moment to get into UEFI booting off GPT discs 
> - just be able to fire up the initial bits of Grub from my MBR disc and 
> have the option of booting Windows 7 off MBR or Ububtu off GPT.

Dual boot on BIOS is inherently limited because only one OS can "own" the MBR 
bootstrap code region, and thus there is only one bootloader. Yes, GRUB can 
chainload the Windows bootloader, so that's how you'd have to do it.

The alternative, which I think is much easier for narrow use cases, on UEFI: 
UEFI install Windows 7 and Linux. And instead of GRUB EFI, use either gummiboot 
or rEFInd as the EFI boot manager. Either one will run the Windows boot loader 
which then boots Windows; and can be configured to scan dynamically for a linux 
kernel. Since kernel 3.3.0 there is a built-in boot loader called EFI STUB, and 
gummiboot and rEFInd can directly boot linux using EFI STUB. You don't need 
another boot loader. And the configuration files are straightforward.



> Now the 3TB [when did the notation move from GB to GiB?] permanent data 
> disc has turned up I need to move my partitions across from an MBR disc to 
> a GPT disc but keep the booting organisation effectively the same.

Windows will not boot from a 3TB drive on BIOS computers. Period. You have to 
enable UEFI and reinstall Windows 7 to use that 3TB drive. Or use MBR and forgo 
1TB.

> I could start all over again, have the 3TB disc as my main disc, UEFI 
> booting with GPT, and use the SSD as a cache.

Make the SSD bootable, and put apps on there as well. Use the 3TB for big files 
like music, pictures, movies, for which the HDD speed is plenty.


> I am starting to suffer temptation to convert the SSD from MBR to GPT, 
> change the BIOS settings to UEFI, and go all modern.
> 
> Time for bed, I think.

Yeah. You'll want to find out what the state of EFI support was for Windows 7. 
It first appeared in Vista, wasn't so great apparently. And I guess it's hit or 
miss with Windows 7. e.g. there's a sizable group trying to get Windows 7 to 
EFI boot on Macs, instead of using the CSM-BIOS (sometimes referred to as Boot 
Camp, in part) and it's much more difficult to hack and make it work, than 
Windows 8 EFI booting on the same Apple hardware. So there's some improvement 
with Windows 8 and UEFI, but I don't know more than this. Windows 7 EFI ought 
to work though.


Chris Murphy