Re: support for partitioned linux md devices

[Bendtsen, Jon]

On 23/08/2012, at 10.59, Miquel van Smoorenburg wrote:
> 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.


sounds reasonable, thank for taking your time to explain why it is a good thing.