On 06.10.11 17:04, Pieter de Goeje wrote:
The layering *is* correct and you *can* create a GPT inside a glabel
label, but then
1) you get device names like /dev/label/somethingp1,
/dev/label/somethingp2, etc.
.. and, you overwrite the last sector of the device, not of the
provider. This is incorrect layering -- GPT should see only the provider
it was given and nothing at different layers.
If you stack GPT on top of glabel, then your statement is not true. GPT will
overwrite the last sector of the (glabel) provider, not the underlying device.
There is no layering violation.
I stand corrected. Sorry for creating confusion with this statement.
Most of the time I was blaming GPT, I was actually blaming GLABEL (see
below)
Because physically the first sector of the device is still GPT data the BIOS
will still try to boot from it, hence it would probably be wise to disallow
GPT on anything other then raw devices.
Yes, but.. what is a raw device? Probably disallow GPT on devices that
are not bootable, but how this can be indicated? GPT is very useful for
it's ability to create labeled partitions.
This problem wouldn't exist if geom classes would write their metadata to the
first sector, but then you could no longer boot from for example
gmirrored/glabeled devices with a MBR.
We seem to blame GPT here, but it is really GLABEL the culprit here.
If GLABEL writes to the first sector of the provider and that makes the
disk non-bootable, then there is little chance that somebody will try to
use first GLABEL, then GPT etc and create the current situation.
Unfortunately, the GLABEL + GMIRROR setup is so common..
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