[ubuntu-uk] Switched hard drives

Andrew Oakley andrew at aoakley.com
Mon Feb 25 14:24:57 GMT 2008


Andy Watts wrote:
> Chris Rowson wrote:
>>>>> l have 2 hard drives in my machine, 1 with windows 2k and the other with
>>>>> Ubuntu on it. l've tried having them both connected to the same ribbon
>>>>> and rebooting with either of the 2 hard drives powered. Sadly it doesn't
>>>>> seem to work so l wonder whether there's a solution..Both drives are set
>>>>> as masters.. l don't want to have both OSs on the same hard drive

Okay, that tells us what you DON'T want to do. ;-)

What is it that you DO want to do?

* Dual boot using separate hard drives?

* Have removable drives?

* Something else? What?

Also... are you using IDE/ATA drives (wide flat ribbon) or SATA (thin 
cable)?

>> I'm assuming you've got a boot loader (Windows - NT loader I think? -
>> or GRUB for Linux) installed on one of the hard drives. You'll need
>> this on the bootable drive so that your PC knows where the operating
>> system resides.

I think Andy might be trying to switch off (electrically) one or other 
IDE hard drives... if so, a boot loader on only one of those drives 
won't help.

I suspect Andy is fundamentally misunderstanding the relationship 
between master/slave and boot options. I suspect Andy thinks a drive has 
to be master to be bootable (which is incorrect).

> l did try setting both to masters, installing a switch on the -ve rail 
> of the 2 molexes. Sadly it didn't work :(

Yeah, that really won't.

Why have you set them both as masters on the same cable?

* You want removable drives (because you're clever, and you might want 
to move the drive to another PC one day), or you want to be able to 
entirely switch off a drive (because you're trying to run on the 
absolute minimum current draw, perhaps because your machine is running 
from 12V DC battery such as a car or van, or because you're just REALLY 
stingy with the electricity bill)

In this case, buy a removable drive caddy or a USB external drive 
enclosure. Removable caddies are about ten quid and fit into a 5.25" 
CD/DVD slot.

(Note that the environmental cost of manufacturing the caddy will vastly 
exceed the environmental cost of leaving the second drive switched on, 
in case you think this is some kind of "green" option; unused drives 
will switch into low-power mode anyway)

* You want to dual boot in the traditional manner

Set one as master and put your boot loader on it, such as GRUB. 
Configure this one boot loader to offer the option to boot off either 
drive. See the GRUB documentation or ask here for more help configuring 
GRUB across two drives (clue: HD0, HD1).

Set the other as slave. You won't need a boot loader on the slave, since 
the boot loader on the master drive will be able to boot off either 
drive (and indeed off any other connected bootable device).

* You want to dual boot through BIOS (because you hate configuring boot 
loaders, and your BIOS offers a simple boot menu such as Dell's F12 
option, and you're just a bit awkward like that)

Set one as master and the other as slave. The BIOS boot options will 
allow you to boot off drive 0, drive 1 etc.

Note that this still won't allow you to switch off the unused drive 
whilst the PC is running. But it will allow you to remove/disconnect the 
  slave drive (but not the master) once the PC is switched off.

* You don't want removable drives but you are determined to have two 
bootable drives that are masters (because both of the hard drives have 
had their master/slave jumpers permanently forced into the master 
position in an unfortunate but surprisingly selective accident with a 
soldering iron / tube of superglue / welding rod, OR, your hard drives 
are set to master by default and you've lost the jumpers)

Install the drives on separate cables. Change the jumpers on your CD/DVD 
drive to be a slave.

(I have some spare hard drive jumpers if you want one? Send an SAE to A 
Oakley, 7 Frampton Cottages, GL20 8NX)

-- 
Andrew Oakley




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