RES: RES: RES: AS2105-based enclosure size issues with >2TB HDDs

Alfredo Dal Ava Junior
2014-08-25T20:44:32Z

On Mon, 25 Aug 2014 Alan Stern wrote:
> Part of the problem is that usb-storage has no way to know that anything
> strange is going on. It's normal for READ CAPACITY(16) to fail (this depend on
> the SCSI level), and it's normal for the READ
> CAPACITY(10) to report a value less than 2 TB.
> Really there is only one way to know whether the actual capacity is larger
> than the reported capacity, and that is by trying to read blocks beyond the
> reported capacity -- a dangerous test that many drives do not like. (And in
> most cases a futile test. If a device doesn't support READ CAPACITY(16), how
> likely is it to support READ(16)?)
> Yes, in theory you can believe the value in the partition table in preference to
> the reported capacity. But what if that value is wrong?
> And how do you tell partition-manager programs what the capacity should be
> when they modify or set up the initial partition table?

We may add this device to UNUSUAL_DEV list, to keep using READ_CAPACITY(10) and
pass some flag to bypass EFI GPT partition check. I'm almost sure that kernel will be able
to mount the partition if we can make it available on /proc/partition. This would make this
device behaves like it does on Windows 7.

I see this as best effort workaround for a cheap buggy hardware, like many others on
UNUSUAL_DEV list

> Attaching the drive over a SATA connection when you want to partition it
> isn't a very satisfactory solution. After all, if you have a SATA connection
> available then why would you be using a USB enclosure in the first place?

You may want do a backup or plug it in a laptop, for example.

[]'s
Alfredo