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#18019
bug-parted Digest, Vol 140, Issue 9
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On 07/14/2014 12:01 PM, Phillip Susi <psusi <at> ubuntu.com> wrote:
>>
>> I find this logic troubling. It's rather similar to the logic that
>> lead to parted using the pre-existing Microsoft basic data GUID
>> when making Linux partitions on GPT disks; out of a pool of just
>> under infinite alternative GUIDs. "Oh it doesn't really matter" on
>> Linux, but meanwhile on dual boot systems, Windows recognizes its
>> partitiontype GUID, but not the contents of the partition, and
>> actively invites the user to reformat it.
>
> How is this at all related? Windows already ignores 0x83.
It does with the default set of drivers. What if somebody loads a Linux
filesystem driver, though? I don't happen to know what actually happens
in this case, but that's (partly) the point: When you set inaccurate
data, you can't predict what will happen with some random tool with
which you're unfamiliar.
> Suggests? Lieing? To whom? Nobody pays attention to the type codes.
The Linux kernel doesn't, but there are at least two other cases to
consider:
* Non-kernel tools might care about the type code. In fact, Chris quoted
the mdadm man page earlier in this thread, and it explicitly states
that it DOES care about the type code!
* Other OSes do check the type code, and if some non-Linux driver or
utility behaves in a particular way based on the type code, setting
something inappropriate invites problems that we can't predict.
> Also if you really want a different type code for raid, there already
> is one: 0xFD.
That's not what the modern version of mdadm wants, though.
In an ideal world, of course, the mdadm developers wouldn't have changed
their tools' expectations from 0.9 to 1.0; but they did, and that means
that the tools that actually set the partition type codes must adapt.
All that said, there is a further complication, and this one isn't
parted's fault: The 0xDA type code that's suggested by the mdadm man
page is NOT specific to Linux RAID. According to
http://www.win.tue.nl/~aeb/partitions/partition_types-1.html, it refers
to "non-FS data"; and according to
https://en.wikipedia.org/wiki/Partition_type, it can be that or a
Powercopy backup. There may be other specific tools that use it, too.
Thus, I'd be a little wary of just switching 0xFD to 0xDA as the MBR
RAID flag in parted. IMHO, what's needed is some coordination between
mdadm, parted, fdisk, and gdisk authors to settle on a standard for this.
--
Rod Smith
rodsmith <at> rodsbooks.com
http://www.rodsbooks.com
This bug report was last modified 10 years and 338 days ago.
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