On Wed, 2011-01-05 at 14:28 +0000, Bryn M. Reeves wrote:
> On 01/05/2011 01:21 PM, Matthew Saltzman wrote:
> > I don't think so. For Anaconda (the installer), a software RAID device
> > is a collection of partitions, one per disk. You can't create the RAID
> > device unless you already have partitions on the disks designated as
> > RAID.
>
> In the context of a setting things up during a Fedora installation this is
> correct but it's important to realise that this is just how Anaconda treats
> software RAID - it doesn't expose the full set of functionality that the kernel
> and mdadm provide.
>
> MD itself does not restrict you to using partitions (rather than whole disks) to
> assemble arrays unless using kernel based auto-detect where array members must
> be primary MSDOS partitions with a partition type of 0xfd. This is no longer the
> default on Fedora.
>
> > Once you have a RAID device, you treat that like a partition on a single
> > disk--create a filesystem or a LVM physical volume on it. It might be
> > the case that you can partition a software RAID device, but I haven't
> > tried that and it doesn't sound right to me. Instead I made a RAID
> > device for each "partition" that I wanted.
>
> This is actually how I tend to do it (on workstations and servers using MD) but
> the Linux MD RAID stack has supported partitionable array devices for years (see
> the mdadm man page option -a/--auto).
>
> The functionality isn't as widely used as the familiar non-partitionable devices
> and isn't supported by many higher-level tools like Anaconda
>
> > Right, but I understood your question as whether a RAID device can
> > contain partitions. That's what I don't know, but I don't think so.
>
> You used to need to set them up manually (although since 2.6.28 all MD devices
> are partitionable afaik), e.g:
>
> Get some test devices:
> # for i in {0..3}; do
> dd if=/dev/zero of=/tmp/img$i bs=1M count=64;
> losetup /dev/loop$i /tmp/img$i;
> done
>
> Create an array and partition it
> # mdadm -C /dev/md3 --auto=mdp -l5 -n4 /dev/loop{0..3}
> # fdisk /dev/md3
>
> Check for partition devices
> # ls /dev/md3*
> /dev/md3
> /dev/md3p1
> /dev/md3p2
> # grep md3 /proc/partitions
> 9 3 196416 md3
> 259 0 15998 md3p1
> 259 1 180416 md3p2
>
> I've seldom actually used this in practice as it's typically more fiddly than
> the non-partitioned equivalent but there are situations where it can be useful
> (generally when I need to simulate some external storage that "must" be
> partitioned using Linux MD devices).
>
> Regards,
> Bryn.
Thanks for the education!
IIRC, the original question had to do with a new install of F14, in
which case Anaconda is probably the tool the OP is expecting to use. I
understand that doing what you describe would require taking care of
building the RAID outside of the install process, either with a live CD
or in the installer's shell on VC2 (if the tools are even available
there).
I also agree that it's unnecessarily fiddly if you don't know that you
need to handle it that way. I prefer to work with the tools provided
when I can, rather than fight them.
--
Matthew Saltzman
Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs
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