Date: Thu, 06 Oct 2011 16:59:00 +0300 From: Daniel Kalchev <daniel@digsys.bg> To: Pieter de Goeje <pieter@degoeje.nl> Cc: freebsd-current@freebsd.org Subject: Re: RFC: Project geom-events Message-ID: <4E8DB424.6050106@digsys.bg> In-Reply-To: <201110061604.15036.pieter@degoeje.nl> References: <1927112464.20111004220507@serebryakov.spb.ru> <j6k7cm$mv0$1@dough.gmane.org> <4E8DA257.9080406@digsys.bg> <201110061604.15036.pieter@degoeje.nl>
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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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