LVM + dmraid

[Phillip Susi]

David Abrahams wrote:

> 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?

The key issues for me are the ability to dual boot with windows, and to 
boot from a raid0 ( stripe ).  With mdraid you can only boot from a 
normal partition or a raid-1, and if the primary disk fails, the system 
will not boot until you manually remove the failed disk or direct the 
bios to boot from the other disk instead ( you DID manually copy the 
boot partition to the second disk right? ).

>> 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
> 

Ok, what is the device name that corresponds to /?  It needs to be 
passed to the kernel in the root= parameter.

> /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 :)
> 

It does not describe the specific parameters that YOU used.  The 
examples given in the howto only apply to the specific partition layout 
that I had, you are supposed to modify it to match your layout, not copy 
verbatim.

>> 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're welcome.


> 
> 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.
> 

Which is why it sounds like you are mounting the wrong root filesystem. 
  If you were mounting the root filesystem it should contain at least 
direcories for /dev, /sys and /proc.  Since this filesystem is empty ( 
save for lost+found ) it must be one of the other filesystems you 
created ( maybe /var? ).


> 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.
> 

It does appear to be handy in terms of ease of use, but resizing 
partitions and snapshotting can be done without LVM if you wish.  I 
chose not to use it mainly so that I can boot directly from the raid ( 
no non raided boot partition needed ) and dual boot with windows ( it 
doesn't understand LVM ).