Large hard drives not recognizing full capacity in some enclosures (#3)

We continue to cover on an issue where using certain enclosures for large hard drive can result in some of the drive's capacity not been seen.

In many cases, this issue is caused by the fact that the original ATA standard limited hard drives 128GB (using LBA). Most modern hard drives use the LBA48-enabled (a 48-bit standard for addressing hard drives) ATA standard in order to access data past 128 GB. If the system is not made aware of the LBA48-capability, the drive reverts to "compatibility" mode, restricting itself to 128GB.

Unfortunately, as noted in our previous coverage, manufacturers usually offer only Windows-based disk utilities that can reset the disk back to its full capacity -- we've yet to find a Mac OS X utility that can provide the same functionality.

Your best bet is to buy an enclosure that that expressly includes large disk support.

One MacFixIt reader, Michael Bramley, writes:

"If I remember the specifics correctly the drive was the fist one to break the 128gb barrier at 160gb, Maxtor put some undocumented features into the ATA command specs and then used a special hacked version of the Oxford Semiconductor 911 firmware to use that drive in an Maxtor branded FW enclosure. Later versions of the 911 where modified by Oxford Semiconductor to use any 48bit/ATA 6 drives and this can be seen by the color of the PCB in the enclosure, red is big drive capable, blue or green is 128gb or less unless using a Maxtor DiamondMax 9 and a hacked version of the firmware.

"Thus if you had an early 911 chip, in a Maxtor branded case using a Maxtor DM 9 with the hacked 911 firmware you'd see >128gb, if you then put a 250gb Seagate in this case, the hack is now useless and you are then subject to the limitations of the 911's ATA 5 spec and less then 128gb."

MacFixIt reader Russ Beckner adds:

"I also had a 250 GB drive that got reformatted to 128 GB by using an older FireWire case. The only way I could format it back to 250 GB was by putting it in a USB 2.0 case and then reformatting on a Windows machine. I have been able to relocate the directory on some crashed FireWire drives by using the USB 2.0 case on my Macs."

Feedback? Late-breakers@macfixit.com.

Previous coverage:

• Large hard drives not recognizing full capacity in some enclosures (#2)
• Large hard drives not recognizing full capacity in old enclosures -- fix

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