[clug] Dumb user question: 2+TB disks, MBR & BIOS...

Michael James clug3 at james.st
Tue Jan 1 23:57:56 MST 2013

On 02/01/2013, at 4:48 PM, steve jenkin wrote:

> My apologies if this question has been asked/answered on-list,
> especially if by me :-(
> My memory isn't what it used to be: once it was reliable.
> I read a piece by Seagate that MBR (Master Boot Record) partitioned
> disks only have 32-bits for sector size, so for 512by sectors, maxx out
> at "2.1TB" (2TiB or 2^41by).
> They said:
> - To boot from them, need an EFI/UEFI system. BIOS won't work unless
> you 'destroke' the drive.
> - Windows XP will only see the *excess* over 2TiB [wrap-around problem]
> - Vista/Win-7/Win-8 can do Maths on >32-bits!
> - If you want to partition the disk you need to use GPT
>   (GUID Partition Table)
> Questions:
> - anyone built any desktop systems with a 3/4TB drive?
> - booted from a large drive? Tips & Tricks?
> - Used 3/4TB drives as (USB) removable Storage?

Yes, MBR (msdos) partition tables can't describe a partition greater than ~2TB.

For a single data partition you __could__ use the whole device
 ie:   mkfs.ext4  /dev/sdb   but I think that's a scary idea.

So GPT partitioning is the way to go, much more modern table structure.
GPT partitioned disks can be BIOS or EFI booted,
 all modern GRUBs have the patches to support BIOS booting.
There is a gotcha, you need a small partition first on the disk to put the intermediate grub stages.

See this for a good discussion of GPT partitioning:    http://www.rodsbooks.com/gdisk/


Michael James				Michael.James at csiro.au
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