MBR partitions on big drives

[Mac the Knife]

Using MBR, could I create four 2TB primary partions on a hypothetical 8TB drive?

Again, with MBR and a hypothetical 8TB drive, could I create a 2TB primary partition and an extended partition divided into three 2TB logical partitions?

I think the answer is yes but I'm not sure.

Yes, I know GUID is a better idea for big drives now but I'm just curious

Mac

:confused:

(I prefer to use one physical drive for the OS and another mirrored one for data - if I'm limited to one HDD then I usually create 2 primary partitions, one for the OS and the other for data, even in Linux)

[Saab Dastard]

Mac,

I don't think that you can do that.

On an MBR disk the partition length and partition start addresses (in sectors, hard limited to 512B / sector) are stored as 32-bit quantities, so it isn't possible to address the start of a partition beyond 2TB, therefore using MBR the disk "appears" to have a max total size of 2TB* - it can't "see" beyond that number of sectors.

* actually 2TB - 512B

Unless you are creating a RAID array, I think that your 8TB is still (just) theoretical. I'm not aware of a single 8TB disk being available (yet), the largest currently is 4 - as I'm sure you are aware.

I have tested in the past just to see what happens with a RAID array and single logical disk > 2 TB (2.5TB - 6 x 500 GB disks RAID5) with Windows Server 2008 installation & partitioning - I don't recall exactly what was shown at the partitioning screen, but I do recall that it was not possible to create a partition > 2TB, nor was it possible to "see" the unused space after creating a partition with the maximum allowable size.

SD

[mixture]

Again, with MBR and a hypothetical 8TB drive, could I create a 2TB primary partition and an extended partition divided into three 2TB logical partitions?

In the world of Microsoft, I would suggest following the KISS principle and therefore I wouldn't necessarily condone confusing matters using such a roundabout partitioning scheme.

[Mac the Knife]

Thanks mix - Please note the "hypothetical"; I wasn't suggesting for a moment that anyone should do this.

Just, for curiosity sake, trying to to get my head around the deeper structure of the MBR.

:8

[Saab Dastard]

Mac,

I'm not sure what your question is. Yes, before LBA the size of HDDs was really quite small! I remember my first PC in 1993 had a 100MB HDD. 1GB was server-size! 4GB was what we built RAID arrays on.

There have been a whole raft of "limits" on HDD sizes that have been overcome as the areal density just kept climbing.

But now we are into the TB range, 7.8GB is very small beer indeed - and LBA has rendered that particular limit nugatory.

This is a very useful piece on the 2TB limit: Understanding the 2 TB Limit in Windows Storage - Ask the Core Team - Site Home - TechNet Blogs (http://blogs.technet.com/b/askcore/archive/2010/02/18/understanding-the-2-tb-limit-in-windows-storage.aspx)

SD

[Mac the Knife]

Well, here is the final word from Dan Starman, a partition guru.

Hello ******,

No. The 32-bit limitation for the Starting Sector of any partition (Primary or Logical) would absolutely preclude being able to partition an 8 TB disk drive using the MBR partitioning scheme!

Theoretically, you could fill the size of a first primary partition with close to 32 bits then use that for where a second primary partition starts and set it for up another 32-bits, which should give you close to 4 TB of overall capacity. (You wouldn't be able to have a 3rd Starting Sector that was over the 32-bit value of 4294967295 sectors though; which is about 2.2 TB. So, you're stuck with a maximum of only two partitions!) I wrote "theoretically" because I haven't had access to even a 3 TB disk drive to test what would happen if I did so... I have no idea if the Windows 7 Pro OS would even allow you to access any part of a disk over 2.2 TB if you set one up that way. And if it did, or did not, you should/would also have to test other OSs and various programs which interact with the file systems on a such a disk drive.

TheStarman.

Interesting, I guess that confirms what Saab said and puts the issue to bed.

Mac

:8