On 23-08-12 10:34 AM, Bendtsen, Jon wrote:
On 23/08/2012, at 09.58, Miquel van Smoorenburg wrote:
I've also filed this as a debian bugreport,
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=684713
Linux md raid array devices come in two flavours: partionable
(/dev/md_d0) and non-partitionable (/dev/md0). Or at least,
that used to be the case, until kernel 2.6.28 where the two have
been consolidated. Now all md devices can have partitions.
However, there is one minor oversight/bug in the kernel: the
sysfs "range" key is still set to "1" for md devices. That means
libparted thinks that it's not possible to partition that device,
when in fact it is.
Which arguments are there for partitioning a software raid device?
Well, first, because you can.. I have been running my personal server on
a partitioned md device (raid1) for a few years now.
But the actual use-case here is Intel Matrix Raid ("imsm") support. Imsm
is a form of sataraid/fakeraid/biosraid that is supported by quite a few
systems. And this is supported by the Linux md driver (and "mdadm") as
well. The md device is then just the "system disk", and it has a
partition table.
The md driver has support for DDF formatted disks (industry standard
portable RAID layout) too. a DDF raid array will often have a partition
table as well.
As you can see in the debian bugreport, I enabled support for this in
the Debian installer for the upcoming "wheezy" release, which turned out
to be trivial - all parts were already there, it needed just a few
fixes. One of the fixes is for libparted, which is used by the partition
manager of the installer, so it works on a partitioned md device.
Thanks,
Mike.
