It might be more than that. What kernel are you using? I have a disk that 
is big too but the READ CAPACITY(16) doesn't fail (this is not a USB 
device);

sdb : very big device. try to use READ CAPACITY(16).
SCSI device sdb: 5651496960 512-byte hdwr sectors (2893566 MB)
SCSI device sdb: drive cache: write through
  sdb: sdb1

I had to use parted to setup a gpt (GNU Parition Table IIRC). grub doesn't 
understand this though (at least I don't think so) so I had to split the 
large array into a small disk (100GB) for the system and a large disk at 
the hardware RAID level. You won't have that issue though if this is just 
an external disk.



On Tue, 2 Oct 2007, Randy Dunlap wrote:

quoted text
> On Tue, 2 Oct 2007 14:11:23 -0700 Richard Sharpe wrote:
>
>> Hi,
>>
>> I hope that this is not an oft repeated question, but recently during
>> testing we encountered the following errors:
>>
>> Oct  2 18:43:12 red-gemini mail-notification: No worthy mechs found
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] Very big device.
>> Trying
>> to use READ CAPACITY(16).
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] READ CAPACITY(16)
>> failed
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] Result:
>> hostbyte=DID_ABORT driverbyte=DRIVER_OK,SUGGEST_OK
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] Use 0xffffffff as
>> device size
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] 4294967296 512-byte
>> hardware sectors (2199023 MB)
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] Write Protect is
>> off
>> Oct  2 18:45:55 red-gemini kernel: sd 7:0:0:0: [sdb] Assuming drive
>> cache:
>> write through
>> Oct  2 18:45:55 red-gemini kernel:  sdb:
>>
>> I think we were returning 0x67FFFFFFF as the max LAB in the READ
>> CAPACITY(16).
>>
>> Is there something special we need to enable in Linux to allow for more
>> than 2TB on a USB device?
>
> There was a mail thread on linux-kernel mailing list just a few days
> ago ("Truncated Filesystem").  The short answer is that MS-DOS
> style partition tables have a 2 TB limit.  There are at least
> 2 ways around that.  One is to use device mapper to group multiple
> partitions into a larger logical device (I don't know details of
> how to do this).  The other that was suggested in that thread
> is to use 'parted' to make the partition(s) instead of using
> fdisk (or sfdisk or cfdisk).
>
>
> Here's the lkml thread:  http://lkml.org/lkml/2007/9/28/387
>
> parted is here http://www.gnu.org/software/parted/index.shtml
> if your distro doesn't have it.
>
> ---
> ~Randy
>
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