Seeking (somewhat) better explanations about supporting > 2.1 TB hard drives.
- by irrational John
Today while Googling about I stumbled across posts claiming that Seagate plans to ship a 3TB drive sometime later in 2010. Unfortunately, the stuff I looked at all seemed to contain tidbits of info which I didn't think fit together properly. (I would link to some examples, but I'm only allowed 1 link per post at the moment).
Now I really don't have any "need" to better understand the underlying tedious details of this. I am just curious. And confused.
So ... some questions I'm hoping someone better informed than I might answer.
The talk about a potential addressing problem in both the hardware and the software confused me. The assertion is that something called something called Long LBA addressing (LLBA) is needed in the Command Descriptor Block as a way to get around the current limits to access a hard drive bigger than ~2.1 (or ~2.2?) TB.
OK, fine. But I thought the last time this problem came up it was solved by extending the length of the LBA field from 28 to 48 bits. (Remember this website? www.48bitlba.com) A 6 byte LBA is clearly large enough, so what's up with this LLBA talk. I thought this was all fixed back by Win XP SP2, if not sooner? And certainly all the hardware should be up to the task, shouldn't it?
The real problem as I understand it with drives much bigger than 2 TB
are the 4 byte LBA fields in the Master Boot Record (MBR) used
to partition just about all hard drives at the moment. The most
likely solution is to migrate to Intel's GUID Partition Table (GPT). A
GPT uses 8 byte fields for the LBA.
What I don't understand in this context is what is the problem with booting say Windows from a 3TB drive that uses a GPT. Granted, the current PC BIOS wouldn't know how to recognize or work with a GPT. But every GPT comes with a so-called "Safety" or "Guarding" MBR in sector 0.Apple already uses a hybrid version of the MBR to allow them to boot Windows on their Intel Macs (aka Boot Camp). Couldn't something similar be done to allow the PC BIOS to recognize and boot from a partition in, say, the first 1 GB of a 3GB or larger drive?
I've got more questions such as where do 4K sectors fit into all of this. But it's probably time I just shut up and posted this. ;-)
-irrational john
