Re: Any pros or cons of using full disk versus partitons?

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On Thu, 14 Apr 2011 18:11:59 +1000
NeilBrown wrote:

> On Thu, 14 Apr 2011 11:57:47 +0400 CoolCold wrote:
>=20
> > Just my 2 cents: I've faced problems when newer disk was smaller than
> > old disk two or three times, so using partitions now with setting some
> > free space at the end - something near 80 or 100 megabytes.

There are also some Gigabyte motherboards which like to cut off a small
portion of a disk at the end via HPA, and writing a backup of their BIOS th=
ere.
https://encrypted.google.com/search?q=3Dgigabyte+bios+hpa
If you had your user data or mdadm metadata there, bad luck.

On earlier motherboards this was done automatically to every new disk on
SATA0, on newer ones I think it's optional and can be disabled. But anyway,=
I
now prefer to leave about 8 MB of space at the end of each drive
unpartitioned, just in case.

And another point, again related to buggy BIOSes: some of them seem to read
first sectors of all attached disks and expect to see an MBR-style partition
table there; and if there's something else instead (e.g. basically random
data, in case of the whole disk used for RAID), they may become confused and
lock-up at boot. I had a couple of such cases where a board would lock-up
at HDD detection with a certain drive attached, and would only boot up
properly after it was zeroed and repartitioned.

>=20
> You don't need partitions to do this. Just use the --size option to mdad=
m.

But then the 1.x+ metadata is still stored at the very end of the device,
which makes it vulnerable to the HPA problem described above.

--=20
With respect,
Roman

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Re: Any pros or cons of using full disk versus partitons?

On Thu, 14 Apr 2011, Roman Mamedov wrote:

> But then the 1.x+ metadata is still stored at the very end of the
> device, which makes it vulnerable to the HPA problem described above.

That's why I prefer v1.2 superblocks, it's stored safely away from MBR
overwrites, but still not at the end.

Quoting "man mdadm"

1, 1.0, 1.1, 1.2
Use the new version-1 format superblock. This has few
restrictions. The different sub-versions store the superblock at
different locations on the device, either at the end (for 1.0), at the
start (for 1.1) or 4K from the start (for 1.2).

I consider v1.0 and v1.1 as dangerous because of why you wrote, as well as
accidental MBR writes.

--
Mikael Abrahamsson email: swmike@swm.pp.se
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