Re: Adding partition to expanded drive
Re: Adding partition to expanded drive
- Subject: Re: Adding partition to expanded drive
- From: Stephen Hoffman <email@hidden>
- Date: Mon, 19 Jan 2009 12:48:18 -0500
So, is this a bug in the implementation of GPT, or am I doing
something wrong?
Hard to say.
The EFI/UEFI spec is ill-considered in this area, IMNSHO.
I had several conversations with the folks that were working on the
spec (was implementing GPT on another platform) and there were various
cases where the GPT design falls apart.
Disk devices that present volumes that can expand entirely on-line are
one such area; I haven't looked to see if the specs have gotten around
to recognizing that volumes are increasingly virtual now.
The whole recovery design seems odd. If the primary GPT (the blocks
after the MBR) are stomped on, what are the chance that the rest of
the volume structures are valid; that the rest of the core volume
structures within the partition(s) haven't also been stomped on? (And
what happens when you have three GPT structures during a transition -
the front GPT, old back GPT, new back GPT - what happens when you get
rolling with an expansion and fail; which GPT do you believe, and how
do you clean up?)
And if you're going to do a backup of a critical structure, why at the
back of the disk and not at a known block-offset pattern (look for a
backup every 1001 blocks into the disk, for instance) within the disk?
There have also been versions of EFI firmware on some platforms that
stomped on disks, too; where a non-GPT volume structure is created on
a disk (one that wasn't completely erased) and the console finds the
backup GPT and helpfully stomps on the front of the disk without any
notification to the user. Where the console corrupts a disk.
My vote would be to get rid of the backup GPT entirely. Allow it, but
don't require it. Or use a block offset from within the disk. But
don't ever let the console get "silently helpful" here.
Whoever did the GPT support for this particular case would have to
address this. But it's just not as simple as it looks here - or at
least it wasn't.
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