Re: [gentoo-user] Trouble with backup harddisks

[Michael <confabulate@kintzios.com>]

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On Saturday, 2 May 2020 09:39:12 BST tuxic@posteo.de wrote:
> On 05/02 09:49, Andrea Conti wrote:
> > > I think, I feel better if I repartitioning/reformat both drives,
> > > though.
> > 
> > It's not necessary, but if it makes you feel better by all means do so.
> > 
> > > *GPT/MBR
> > > From a discussion based on a "GPT or MBR for my system drive" in
> > > conjunction with UEFI it was said, that GPT is more modern and
> > > save.
> > 
> > More modern I concur. For the rest it's mainly about features: >2TB
> > partitions and way more metadata, plus not having to bother with CHS
> > values which make no sense in today's drives. And being able to define >4
> > partitions without littering the disk with extended boot records, which
> > is probably the only thing I'd call "safer".
> > 
> > My point was that none of this is relevant in an external drive which is
> > under 1TB and will only hold a single partition starting at sector 1 and
> > spanning the rest of the disk. A system drive, especially if booting from
> > UEFI is a different case for which GPT absolutely makes sense.
> Ok, the other way around: Does GPT hurt more than MBT on a external HD
> used for backup puporses (no boot), has 1T and 1 partion of that size?

Unless you're planning to boot from Windows XP or some antiquated old LiveCD, 
a GPT partitioning scheme is better in *all* respects and it is more robust 
than MBR because:

- The partitioning tables created by GPT are backed up at the end of the disk.
- GPT uses CRC make sure its data is intact, or will warn of corruption and 
attempt to restore from the back up.


> > > My question was meant not so much as "MBR or GPT?"
> > > but more whether there are some variants of GPT (with
> > > protected MBR for example -- which was completly new to me),
> > > which I should use or avoid.
> > 
> > There are really no "variants" of GPT. The protective MBR is only there to
> > make all space in the disk look allocated to MBR partitioning tools that
> > are not GPT-aware, and is automatically written for you by all GPT
> > partitioning tools.
> > 
> > In addition to the opaque entry of type 0xee, this MBR can also contain
> > entries pointing to at least some of the actual partitions; this is
> > called a 'hybrid' MBR and allows MBR-only access to partitions that are
> > within the limits of MBR addressing (start and end sector <2TB). These
> > are only useful in very specific cases an I would consider them a hack
> > more than a solution; while gpt-fdisk has some support for creating
> > hybrid MBRs (don't know about fdisk), you won't get one unless you
> > specifically ask for it.
> Thanks of the information! :)
> 
> > > But: Are rescue systems for USB-stick more UEFI/GPT aware nowadays
> > > or "traditionally" based on MBR/BIOS-boot?
> > 
> > I think that anything that's not ancient will have tools and kernel
> > support for both MBR and GPT, and will boot fine in both BIOS and UEFI
> > modes.> 
> > > One thing I found is really handy: An USB-stick with an rEfind
> > > installation. As long as your PC supports UEFI (or can switched to it)
> > > rEfind is able to boot "everything" without prior configuration.
> > 
> > You can probably do the same with GRUB2, albeit in a way less
> > user-friendly fashion :) But why do you consider the ability to boot
> > anything but the rescue system itself important in a rescue system?
> Recently a BIOS update deleted all UEFI entries and the system no
> longer boots. With rEfind from a USBstick I was able to boot
> the sustem nonetheless and the reinstallation of grub solves
> the problem.
> Task accomplished! :)
> 
> > > Some rescue-system which really shines and with which you have made good
> > > experiences?
> > 
> > My usual go-to is SystemRescueCD (the old 5.x gentoo-based one).
> > 
> > andrea
> 
> Thanks for the info, Andrea!
> 
> Cheers!
> Meino

Any up to date Linux LiveCD/USB should be able to boot your PC and 
automatically recognise its GPT partitioning.

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