[RFC/CFT] Trusty work for dmraid

[D. Jared Dominguez]

>>> DDF1 may be fairly common on servers since this is the usual format
>>> used by server class fakeraid cards, and servers are typically set up
>>> using raid5.

DDF is also commonly used on hardware RAID cards, but the
DDF standard also defines ways to allow for proprietary extensions, so 
it's important to be really careful about checking which hardware is 
supported.

>> Yes, I also thought that ddf1 (apparently Adaptec controllers also tend to use
>> this format) would be the more common.
>>>
>>>> One alternative option would be to check whether mdadm DDF support
>>>> also includes everything that dmraid did. At least a quick test
>>>> with a ddf1 RAID5 which I did set up using mdadm seems to be found
>>>> by dmraid scanning, too. That option would leave us only with
>>>> NVidia controllers depend on dmraid RAID5.
>>>
>>> Last I saw on the linux-raid mailing list they were still shaking a
>>> few bugs out of the ddf support in mdadm.  nvidia controllers seem to
>>> mainly have been used in enthusiast/gamer/workstation desktop boards
>>> where raid0 is far more likely than raid5.

I spent some time a year ago investigating mdadm DDF support, and it was 
definitely not quite ready for prime time then. It's had a huge overall 
over the past year, including adding support for secondary RAID levels. 
When I checked a year ago, it only seemed to support containers created 
by mdadm. Unfortunately, I don't have the fakeraid hardware to check 
what's supported.

 From what I recall, there were also some installer issues, but that's 
all I remember about that. There are definitely still installer issues 
with Intel Matrix RAID.

--Jared


-- 
Jared Dominguez
Linux Engineering
Dell | Enterprise Solutions Group