[Discuss] A BIOS and MBR Question

[John Blomfield]

On 10/07/2014 10:19 AM, brendan wrote:
> have you tried swapping the SATA ports the drives are plugged into? on 
> my machine, there are primary and secondary channels - the primary 
> channel always shows up as the first drive.
>
Yes you can do that on full size motherboards with more than one HD bu 
you can't swap the 2.5" SATA and the mSATA SSD they have totally 
different connectors and housings. My motherboard has just the two 
connectors, mSATA and SATA. It has occurred to me that there may be a 
jumper on the motherboard that has the same effect. I need to get a spec 
for the motherboard; perhaps do that this afternoon.

> or, just boot off a boot cd and use it to install grub on the other 
> hard drive as well. then either can boot and it won't really matter 
> anymore.
I can of course boot off a USB key (My box does not have a CD drive) but 
that's a bit clumsy. As I said I don't have a problem with having the 
MBR on the 2.5" HD and my questions are really academic, basically 
because I want to understand whats going on.

John


>
> On 14-10-07 09:56 AM, John Blomfield wrote:
>> First some history. Sometime ago my old desktop had a HD failure and 
>> I replaced with a 1TB 2.5" HD anticipating that I would want such a 
>> drive if I bought a new bare-bones mini PC which I have now done. 
>> This 2.5" drive contains in addition to an OS some data I wanted to 
>> retain. As I've mentioned before my new mini PC can accommodate one 
>> SSD mSATA drive and a 2.5" HD. Not wanting to be without the use of 
>> my old PC while I configured my new PC I installed just the SSD mSATA 
>> and installed an OS and some data on it first. Having got that 
>> working I then added the 2.5" HD from my old PC.
>>
>> Then I found a problem! The BIOS recognised the 2.5" HD as the first 
>> drive and the SSD as the second drive, whereas, with only the SSD 
>> installed it was the first drive. I tried changing the boot order but 
>> the BIOS still seemed to look for the MBR on the HD not the SSD. My 
>> OS mapped the HD as sda and SSD as sdb and I could not see a way to 
>> change this. I tried changing the GRUB device.map but that did not 
>> work. After a lot of messing around I had to change the GRUB menu.lst 
>> and the /etc/fstab file to reflect the fact that the SSD was now sdb 
>> and not sdb. Also I had to install the MBR on the HD.
>>
>> So my question is: Does the mini PC hardware and/or the BIOS 
>> determine which drive is the drive where it looks for the MBR? And is 
>> it possible to override it and make it look on another drive? Why 
>> does changing the boot order not seem to change this? What's going on?
>>
>> John
>>
>
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-- 
John Blomfield
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Old John B's Linux Notes http://www.oldjohnbslinux.wordpress.com