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Occasional Advisor
OldybutGoody
Posts: 10
Registered: ‎08-08-2011
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Accepted Solution

Exceeding 2Tb limit questions

[ Edited ]

Hi guys,

 

I understand that my 3Tb Mybook Essential exceeds a Tb limit.

 

Would someone point me to a 'nice, friendly, easy to understand' source that can explain this and related issues such as formatting to NTFS, GPT.

 

Be gentle with me.  :-)

 

Thanks

 

 

Honored Contributor
Joe_S
Posts: 5,320
Registered: ‎08-04-2010

Re: Exceeding 2Tb limit questions

I don't know if this will help http://blogs.technet.com/b/askcore/archive/2010/02/18/understanding-the-2-tb-limit-in-windows-storag...  bacically you need GPT instead of MRB abd NTFS, Vista and about is OK but I think Only XP 64 bit will handle it possible update needed.

Joe

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Honored Contributor
fzabkar
Posts: 1,818
Registered: ‎02-06-2010
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Re: Exceeding 2Tb limit questions

WD's 3TB externals are specified to work with Windows XP right out of the box, so, AISI, they must be preformatted with an NTFS file system. The way that WD circumvents the apparent 2TiB MBR limitation is by configuring the enclosure to report that the external mass storage device has a 4KB sector size rather than 512 bytes. This extends the MBR limit to 16TiB.

I hope that made sense. :-)

Frequent Advisor
WDCHDDuser
Posts: 36
Registered: ‎08-10-2011
0

Re: Exceeding 2Tb limit questions

Is there some reason the drive within couldn't actually have 4 kb sectors, i.e. an Advanced Format drive?  Wouldn't surprise me if that's what's contained within the 3 TB MyBook.

Honored Contributor
fzabkar
Posts: 1,818
Registered: ‎02-06-2010
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Re: Exceeding 2Tb limit questions

The drive within the 3TB My Book is indeed a 4KB-sectored Advanced Format drive. However, it still reports to the outside world that it has 512-byte LBAs (logical sectors). WD refers to this as "512-byte emulation (512e)".

Between the drive and the USB port is a USB-SATA bridge chip. This chip enables the drive to communicate over a foreign interface. Simply put, the PC speaks USB, the drive talks SATA, and the bridge IC is their translator.

In the case of the My Book, the bridge also fakes the drive's logical sector size. That is, the bridge reports to the OS that the external mass storage device has 4KB LBAs. Therefore, when the OS writes a 4KB LBA to the drive, the bridge breaks it up into 8 x 512e LBAs, and then writes them to the drive. The drive then takes those 8 LBAs and reassembles them into a single 4KB physical sector. At least that's how I understand it.

If you follow Joe's link, the author writes that the Partition Size Limitation is 4,294,967,295 sectors. This number corresponds to the largest number that can be represented with 4 bytes (= 0xFF FF FF FF). Traditionally, the sector size is 512 bytes, so the total capacity works out to be 2TiB.

However, in the case of the 3TB My Book, the sector size is 4096, so the maximum partition size for an MBR partition is ...

4,294,967,295 x 4096 = 16TiB

Frequent Advisor
WDCHDDuser
Posts: 36
Registered: ‎08-10-2011
0

Re: Exceeding 2Tb limit questions

[ Edited ]

Makes sense.  I was aware of 512e.  I believe it's one of the tricks that was invented to make Advanced Format drives play nicely with Windows XP.

 

I am planning to remove the 3 TB drive from mine and dump the MyBook enclosure for various reasons.  I suppose that means the drive will not work with Windows XP as-is.  But that's OK.  I don't plan to use it with Windows XP at all.  The only OS's I really use any more are Windows 7 and Ubuntu, both of which support Advanced Format drives natively.

Honored Contributor
fzabkar
Posts: 1,818
Registered: ‎02-06-2010
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Re: Exceeding 2Tb limit questions

If you connect your 3TB drive directly to a SATA port, as is , then I expect that Windows will report that it needs to be formatted. This is because it won't find the boot sector in the right place. Furthermore, I expect that Disk Management will report that there is a single 375GB (= 349GiB = 3TB / 8) NTFS partition with the remainder of the drive being unallocated. However, that's only speculation on my part, so your feedback would be most helpful.
Frequent Advisor
WDCHDDuser
Posts: 36
Registered: ‎08-10-2011
0

Re: Exceeding 2Tb limit questions

As a matter of fact, I did have a problem with the MyBook being reported as only ~375 GB.  But it wasn't with Windows itself. 

 

The current free edition of HD Tune (version 2.55) apparently cannot handle drives of this size.  It reports the MyBook 3 TB as only 375 GB, and cannot perform any benchmarks.  An attempt results in an error dialog stating, "Read error!  Test aborted."   HD Tune Pro (non-free, trial edition) has no such issue.

 

I suspect the free edition of HD Tune can only handle MBR disks.  The MyBook must be partitioned with GPT.

 

Once I get the new enclosure, I expect to have to reformat my 3 TB drive, using GPT, because it is presently (and silently) encrypted (this is one reason I'm dumping the MyBook enclosure!).  So it will look like an "unformatted" disk to Windows 7. 

 

Because I have a fairly old motherboard (2007 design), it uses BIOS instead of EFI.  I suspect that I would be unable to boot from the 3 TB drive, due to its use of GPT rather than MBR.  But that is fine, as the drive is only for backup, not OS use.

Honored Contributor
fzabkar
Posts: 1,818
Registered: ‎02-06-2010
0

Re: Exceeding 2Tb limit questions

I'm almost certain your drive is partitioned in MBR mode, not GPT. The way that the My Book circumvents the 2TiB MBR limit is to use 4KB LBAs rather than 512 bytes.

You could easily confirm this by examining sector 0 with a disc editor. It would be most helpful if you could upload its contents.

DMDE (DM Disk Editor and Data Recovery Software):
http://softdm.com/download.html

Occasional Advisor
OldybutGoody
Posts: 10
Registered: ‎08-08-2011
0

Re: Exceeding 2Tb limit questions

[ Edited ]

 

Thanks Joe_S!

 

That was just at the right level!

Appreciated.

 

Pete

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