"Access Mode" question (BIOS)

[The late XV105]

What is "Access Mode" in the BIOS of my ASUS P5N32-SLI motherboard, please?

I ask because I have just cloned the HDD that runs the XP operating system and Program Files of my media server. Initially, swapping out the original o/s HDD and replacing it with the cloned one gave rise to boot failing with "Error loading operating system". I was puzzled because the cloned HDD is a box new and identical Seagate Barracuda (apart from slightly later firmware I see) and I was careful to write the MBR, the boot sector, and the boot.ini.

After logical trial and error I found that I could solve the problem and successfully boot from the clone so long as I followed this process (some details are irrelevant but I include them all to give continuity):


Mount target HDD in external enclosure and connect to PC (I used eSATA)
Switch on media server and enter BIOS
For the target HDD, change Access Mode from AUTO to LARGE
Save changes and boot
Perform a full format of the target HDD
Clone HDD yadda yadda yadda
Shut down media server
Open enclosure and remove cloned o/s HDD
Swap o/s HDD for cloned o/s HDD (in the same bay as it happens)
Restart PC and enter BIOS
For the boot HDD, change access mode from AUTO to LARGE
Save changes and boot
Observe successful boot; all is cushty


If I formatted and cloned the target HDD having booted beforehand as Access Mode AUTO, the cloned result wouldn't work whether set to either AUTO or LARGE when booted for use. Neither would it work if formatted and cloned as LARGE but then booted for use as AUTO. I have to use Access Mode LARGE both before formatting & cloning and for runtime usage.

Why, please, since the donor HDD works just fine with Access Mode AUTO (but I now know won't boot if left as LARGE)?

It's no big deal, and I have a working clone now locked safely away in my employer's backup facility, but I'm curious.

[Avtrician]

When you say cloned, did you use software like Norton Ghost the create the clone, or did you just copy the all files to the new drive?? If so, no boot sector and associated information was created..

[The late XV105]

I'm not that dumb ;)
XXClone.

MBR, boot sector, and boot.ini all successfully written.

Note that the clone DOES boot.

My question is why it only does so when created and used as Access Mode "Large".

[green granite]

You're not alone, looking at various forums lots of people have the same problem.

It appears that in 'auto mode' it selects CHS instead of LBA

[The late XV105]

Thanks, green granite, but with humble respect my question is still unanswered.

Why would a cloned disk be different to its donor? They are the same Seagate Barracuda 7200.12 320GB with 16MB cache. The only difference between the two disks are that the cloned one is running marginally newer firmware and the files on it are physically located differently (as proven by running MyDefrag on the donor before it was cloned and on the clone immediately after the first boot using it).

As well as the fact that the two disks require different Access Modes, I am also puzzled by the fact that Auto doesn't work for the clone; to my simple brain the term Auto implies that the BIOS is able to automatically detect whether CHS or LBA is in use on the boot disk and switch accordingly, whereas Large implies that the BIOS is restricted to using LBA (so won't boot if CHS is in use). My initial setting was Auto, so I presumed that the BIOS was free and able to make a choice. It wasn't until I restricted the BIOS to Large though, that it worked; this appears to be counter-intuitive.

Cheers,
Puzzled of Warks

[The late XV105]

Puzzled of Warks is back.

Perhaps Wikipedia has the answer (http://en.wikipedia.org/wiki/Logical_block_addressing) to both of my questions.

My bold:
"Until the release of ATA-2 standard in 1996, there were a handful of large hard drives which did not support LBA addressing, so only Large or Normal methods could be used. However using the Large method also introduced portability problems, as different BIOSes often used different and incompatible translation methods, and hard drives partitioned on a computer with BIOS from a particular vendor often could not be read on a computer with a different make of BIOS."

I did not partition the clone HDD but some time ago I did partition the donor HDD. When the PC was new I partitioned the latter (donor) HDD as C and D but then changed my mind and completely reformatted it as C before a ground-up rebuild of the O/S. This means that the C partition was created by the BIOS on my PC. The clone HDD however is box-fresh from Seagate; all I have done is format it and then use it as the target to receive a clone.

I guess the proof of the pudding would be to put the clone HDD through the same repartitioning process as its donor, and then reverse it with a full reformat, but what I read on Wikipedia does at least appear to make sense.

A logical interpretation or barking up the wrong tree?

Ta,
XV

[green granite]

Have you tried updating the BIOS to the latest version? My point was that it was probably a BIOS software problem, and possibly couldn't recognize something in the new disc's firmware so it assumed CHS

[The late XV105]

Latest BIOS for this mobo, yes, thanks, gg.

With interest spiked by the Wikipedia statement and with nothing to lose I have


Partitioned the cloned HDD in to two using the same copy of Acronis Disk Director that I had originally used to partition the donor HDD before I changed my mind and started again from scratch. The only difference this time is that the second drive letter was Q rather than D because all the letters in between are now used for other physical and logical drives
Converted both partitions on the clone HDD to unallocated space - again, replicating what had been done in the past to the donor HDD
Switched off the media server
Repeated the cloning operation using the steps listed in my original post apart from those related to changing Access Mode; this time it was left as Auto


Guess what?
Now that the clone has lost all trace of its origins in a Seagate factory it now boots as Access Mode = Auto, just like its parent, and not Large any more.

Seems Wikipedia was right and this is a BIOS compatibility thing.

[Saab Dastard]

Interesting experimentation there, XV, thanks for sharing your experience. :ok:

SD