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Re: USB3 3TB HDD boot

From: Chris Murphy
Subject: Re: USB3 3TB HDD boot
Date: Thu, 14 Mar 2013 20:18:46 -0600

On Mar 5, 2013, at 12:22 AM, Vladimir 'φ-coder/phcoder' Serbinenko 
<address@hidden> wrote:

> On 05.03.2013 00:16, Chris Murphy wrote:
>> On Mar 4, 2013, at 12:43 PM, "Lennart Sorensen" <address@hidden> wrote:
>>> On Mon, Mar 04, 2013 at 08:33:51PM +0100, Vladimir 'φ-coder/phcoder' 
>>> Serbinenko wrote:
>>>> Not necessarily. 3T drives often use msdos, just with 4K sectors which
>>>> increases the range of msdos to 16T.
>>> Hmm, I suppose that would work.  I have never seen one that did that yet,
>>> but I don't have that many 3TB drives either.
>> I wonder what the BIOS does when it "asks" the drive for LBA 0, and receives 
>> 4096 bytes instead of 512 bytes.
> It doesn't get that far. Most likely it bails out after reading SCSI
> descriptor.

I have anecdotal evidence these drives are now in the wild. Mac user with a new 
3TB Seagate USB 3 external drive:
Device / Media Name:      Seagate Backup+ Desk Media

This is not very descriptive. But when I ask the user to display the GPT with 
gdisk, there's normal output, except for this line:
Logical sector size: 4096 bytes

Next, when I have him report the result from:
sudo dd if=/dev/disk3 count=2 2>/dev/null | hexdump -C

The 1st 512 bytes reported is the PMBR, but the 2nd 512 bytes is garbage, not 
the GPT header as expected.

When this drive is connected to the computer and he tries to boot Windows, the 
system hangs at a black screen. That's kinda interesting/concerning, if even 
CSM-BIOS implementations on recent EFI firmware can have problems with such 

Chris Murphy

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