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RE: USB3 3TB HDD boot

From: Elliott, Robert (Server Storage)
Subject: RE: USB3 3TB HDD boot
Date: Mon, 18 Mar 2013 23:26:49 +0000

> -----Original Message-----
> From: address@hidden [mailto:grub-devel-
> address@hidden On Behalf Of Chris Murphy
> Sent: Monday, 18 March, 2013 5:37 PM
> To: The development of GNU GRUB
> Subject: Re: USB3 3TB HDD boot
> On Mar 18, 2013, at 3:46 PM, Vladimir 'φ-coder/phcoder' Serbinenko
> <address@hidden> wrote:
> >
> > BIOS interfaces support up-to 64-bit LBA adressing so >2T is just issue
> > of fixing bugs in BIOS.
> Aha. OK good to know.
> > On, the other hand problem with 4Kn is deeper as
> > it doesn't seem to even be any implicit agreement of how such disks
> > should be handled for booting. Nor does it seem any impmentation on
> > either bootloader or BIOS side.
> This is concerning. So at the moment the 4Kn drives are effectively data only,
> non-bootable. Is it the same situation for UEFI and BIOS? It seems the 4Kn
> release is premature. The 512e method has few downsides for any recent
> partitioning tool, which ensures alignment, and they are also bootable without
> concerns. I'm unaware of a downside.

One reason is that 4Kn forces all I/Os to be aligned, while 512e allows 
non-aligned I/Os.  512e drives are somewhat obligated to ensure that writing 
one 512 byte logical block won't affect the other seven 512-byte logical blocks 
sharing that physical block if a power loss occurs or an error happens; this is 
not simple to do. It is cheaper and easier just to ship the drive as 4Kn and 
force software to adapt.  That's why you are seeing this first in cheap 
large-capacity USB drives.

CD/DVDs use 2048 byte logical block sizes with the CDFS ISO 9660 filesystem, 
and most systems can boot from CDs nowadays, so booting from non-512 byte 
logical block sizes is not impossible.  There's just a lot of legacy BIOS, MBR 
based code that assumes 512 byte logical blocks on hard drives (and 32-bit 

UEFI systems using GPT are likely to support booting from 4Kn drives and use 
64-bit LBAs throughout.  Some OSes already claim boot support from 4Kn drives 
in those systems.  The UEFI spec has included warnings about detecting the 
logical block size since 2006.

Rob Elliott    HP Server Storage

> Chris Murphy
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