Re: LVM + dmraid

Phillip Susi <[email protected]> writes:

> Could you supply some more background information?  

The first piece is that I've now dropped dmraid for mdraid, since I
don't *really* need to dual boot to Windows.  I want to run Windows
virtualized.  Is anyone going to argue that I'm giving up something
important by using mdraid?

> What kind of raid setup do you have?

Onboard NVRaid on a Tyan Thunder K8WE s2895.

> How did you configure LVM?  

Not sure I understand the question.  I followed the
https://wiki.ubuntu.com/FakeRaidHowto which shows how to get dmraid
running from a LiveCD and then I just used fdisk and LVM command-line
tools to set it up.

> What kind of logical volumes did you create within the volume group?

Typical/aggressive arrangement:

/ 100M
/usr 50G
/var (also storing /tmp here) 10G
/var/spool 4G
/var/log 4G
/home 200G
/swap 16G
/usr/local 50G

/boot is on a primary partition outside LVM

> How did you direct the system to boot from the correct root volume (
> root= kernel parameter )?

The FakeRaidHowo tells all.  I really did follow the directions :)

> I have not used LVM before but I have read a good deal about it, but I
> wrote the FakeRaidHowto you followed so I may be able to help.  

Oh!  I've spent many hours with your webpage, so thanks (I think ;->)
for writing it!

You might want to add the following:

To use LVM2 w/dmraid, change /etc/lvm/lvm.conf to include

   types = [ "device-mapper", 254 ]

You'll want to do that in the chrooted filesystem also, of course, so
you do this twice, or you copy the file.

To suppress a lot of warnings about locales, install language-pack-en
immediately after chrooting.

(the 4 July dmraid restart trick works for me too)

> My initial guess is that the initrd is mounting the wrong root
> filesystem, such as your /boot ( which is a regular partition, not
> part of the volume group right? ) 

Right.

> and this partition has no /sys and
> /proc directories, which is why it complains about not being able to
> mount them.

Well, IIRC there was nothing useful mounted on /root.  I don't
remember exactly what it was, but it just contained lost+found.  I can
mount /boot on /root and I see the files.

> By the way, is there a particular reason you want to use LVM over
> dmraid?  I'm not quite sure what benefits it would provide over
> conventional partitioning.

LVM has lots of benefits in terms of flexibility.  It's easy to
non-destructively resize partitions, including extending them into new
disks when you run out of space.  There's snapshotting and many other
useful (-sounding) features.  I'm not an expert sysadmin yet, but I
don't want to cut myself from these capabilities at step 1.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com