Disk Size Variance

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Level 2

205 points

Disk Size Variance

I have two Western Digital Caviar Series hard drives, the 2.0TB and 2.5TB (WD20EARS and WD20EZRX). They're both plugged into a Vantec NexStar dual bay hard drive docking station. When I open Disk Utility under OS 10.8 it shows me both drives, but the sizes are listed as 2.0TB and 2.2TB.

As I understood it, formatting a drive consumed a bit of space, so I can accept that a 2.5TB drive might format down to 2.2TB, but why would that be the case and then the 2.0TB drive actually show 2.0TB of space? As far as I can tell they were partitioned and formatted the same way but it's possible I'm wrong since the 2.0TB drive is older.

If it's not a lot of trouble I wouldn't mind having my 300GB back.

Mac mini, OS X Mountain Lion (10.8.4)

Posted on Jul 28, 2013 2:32 PM

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Answer 1

Jul 28, 2013 2:39 PM in response to Kris Brown

A 2.2TB limit generally means the drive controller being used has a 32-bit logical block addressing (LBA) scheme and is using a 512-byte block size, and 2^32 blocks at 512-bytes per block gives you 2.2TB maximum, regardless of the drive size used (2.5TB, 3TB, 4TB, etc.).

This may be a hardware limit of your NextStar docking station, so one option is to try using another enclosure for the drive.

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Answer 2

Kris Brown Author

Level 2

205 points

Jul 28, 2013 4:23 PM in response to Topher Kessler

your post prompted me to double check the specs on the dock and you're right, it's only listed as working up to 2TB. serious bummer 'cause I thought this would work with larger drives when I bought it.

Any suggestions on a good dual bay 3.5" SATA dock that supports 4.0TB drives? I was planning to buy a couple soon but it looks like I need a new drive dock first.

I'd love to get one with hardware encryption but they don't appear to exist beyond single bay 3.0TB.

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Answer 3

Jul 28, 2013 4:40 PM in response to Kris Brown

Most new ones will do so. There are many out there, but some include those supplied by OWC (http://eshop.macsales.com/shop/firewire/) and NewEgg (http://www.newegg.com/External-Enclosures/SubCategory/ID-92)

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