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Old 12-29-2011, 03:25 PM
"R. G. Newbury"
 
Default Boot Disk

On 12/27/2011 11:21 AM, Jeffrey Ross wrote:


> On Sun, Dec 25, 2011 at 2:37 PM, Jeffrey Ross<jeff@bubble.org> wrote:

>> Is there a way to identify which disk the BIOS is using to boot from (eg
>> disk 0 or 1) when I don't have physical access to the system to view the
>> BIOS settings?



> If both disks have identical bootloaders, I'm not sure there's any way
> from a running system to check which one you booted from. If you
> don't mind rebooting it, you could add a different arbitrary kernel
> argument to the GRUB configuration of each disk's bootloader, reboot
> the machine, then check /proc/cmdline to see which one shows up.



In this case it turns out it was booting off of sda (which is what I
suspected), I ended up taking a ride down to the datacenter and verifying
the BIOS.

The original question although no longer important remains, can you tell
which disk the initial load occurred from? I did run dmidecode and found
nothing of value.


There is a way to determine things remotely, if you do some setup
beforehand.

Your two hard drives are otherwise (I presume) exactly alike.
Set them up similarly, *except* that both use all but a megabyte or so
(or one cylinder's worth of blocks). Make that little extra into a
partition on ONE of the disks.


You can then remotely use 'cat /proc/partitions' to show the attached
drives and partition sizes (or use 'sfdisk -uC -l').


The extra partition will denote which drive is being used as 'sda' or
'sdb'. This method is independent of the contents of the disk.


You may be able to re-size both of them in place although it might
require another site visit. I have NO idea if gparted can be made to
work remotely with vnc etc.


Geoff





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Old 12-29-2011, 03:30 PM
Alan Cox
 
Default Boot Disk

> > which disk the initial load occurred from? I did run dmidecode and found
> > nothing of value.

dmidecode is the wrong interface. EDD provides the drive to BIOS mapping
tables, DMI provides static configuration data.

> Your two hard drives are otherwise (I presume) exactly alike.

Just use the drive serial numbers for that - or the UUIDs of the
partitions - much easier and basically how Fedora itself does it.

Alan
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Old 12-29-2011, 08:59 PM
Aaron Konstam
 
Default Boot Disk

On Thu, 2011-12-29 at 16:30 +0000, Alan Cox wrote:
> > > which disk the initial load occurred from? I did run dmidecode and found
> > > nothing of value.
>
> dmidecode is the wrong interface. EDD provides the drive to BIOS mapping
> tables, DMI provides static configuration data.
>
> > Your two hard drives are otherwise (I presume) exactly alike.
>
> Just use the drive serial numbers for that - or the UUIDs of the
> partitions - much easier and basically how Fedora itself does it.
>
> Alan

Where or how does one find EDD and DMI?
--
================================================== =====================
I dote on his very absence. -- William Shakespeare, "The Merchant of
Venice"
================================================== =====================
Aaron Konstam telephone: (210) 656-0355 e-mail: akonstam@sbcglobal.net

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Old 12-30-2011, 02:02 PM
"R. G. Newbury"
 
Default Boot Disk

On 12/29/2011 11:30 AM, Alan Cox wrote:

which disk the initial load occurred from? I did run dmidecode and found
nothing of value.


dmidecode is the wrong interface. EDD provides the drive to BIOS mapping
tables, DMI provides static configuration data.


Your two hard drives are otherwise (I presume) exactly alike.


Just use the drive serial numbers for that - or the UUIDs of the
partitions - much easier and basically how Fedora itself does it.

Alan


Agreed. But you have to *know* the drive serial number or UUID to do
that. And there is, of course, a high probability that you will not have
that information available.


(Ha! With Captain Murphy's thumb on the scale the probability is
exactly: 1.000000. )


The advantage of marking the actual disk is that you only need remember
which way you installed...extra partition on sda/sata 1 or not.

Geoff


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Old 12-30-2011, 02:10 PM
Alan Cox
 
Default Boot Disk

> Agreed. But you have to *know* the drive serial number or UUID to do
> that. And there is, of course, a high probability that you will not have
> that information available.

It's in procfs, sysfs, ioctls and via dmesg. It's not hard to get at !
and if you are doing it in advance you can also use labels which are even
easier to remember than uuids

Alan
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Old 12-30-2011, 02:15 PM
Frank Murphy
 
Default Boot Disk

On 30/12/11 15:10, Alan Cox wrote:

Agreed. But you have to *know* the drive serial number or UUID to do
that. And there is, of course, a high probability that you will not have
that information available.


It's in procfs, sysfs, ioctls and via dmesg. It's not hard to get at !
and if you are doing it in advance you can also use labels which are even
easier to remember than uuids

Alan


If the labels are worn off / inaccessible
you can install hardware lister:
yum install lshw (lshw-gui)
which will return the serial numbers.


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Frank Murphy
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