[ydl-gen] Re: YDL 4.1 Installation: Creating software RAID

[Alexander Holst]

On Fri, 2006-01-20 at 02:13,
yellowdog-general-request at lists.terrasoftsolutions.com wrote:

> Considering a PC partitioning scheme on a PPC system defeats the 
> purpose of why you are using a PPC system in the first place.  Leave 
> that stuff for Intel based architectures.

Unfortunately, as for the software raid tools included in the Linux
kernel as well as the userspace tools, to create the raid partitions
successfully, they both do expect a PC style partition table - I assume
they were originally written for Linux on x86 architecture.

Even though it sounds weird, but PC style partition tables work with
Linux on a PPC just as well as the Apple style partition table do. OSX
on a PPC might be a different story however.

> Technically arguments can go one way or another, 

> [... snip philosophy lesson ...]

> No one I've met would try to apply badmington rules in baseball, and 
> likewise it is between PC/Intel engineering schemes and PPC engineering 
> schemes.  The difference between the architectures and how they access 
> peripherals could fill books; that's another story.

Derrick, please read the manuals for creating a SOFTWARE RAID on Linux -
they clearly state, that some features of these tools ONLY work with PC
style partition maps - especially the auto detection and mounting at
startup. They need special flags to be present which can't be set on Mac
style partition tables.

I have to admit though, that my last RAID I build was with a 2.4.22-2g
kernel on YDL-3.1 - however, I doubt, that the development community of
the raid tools has fully implemented Mac [or better say Apple] style
partition tables as of yet.

> Onto something a bit more useful to you.  TSS does provide this 
> information regarding RAID setup in the ydl.net service.  You can read 
> more about the offering here:
> 
> http://www.terrasoftsolutions.com/support/solutions/y-hpc/

Unfortunately, all I can see there is the hint that YDL.net will provide
some info on how to set up an "Apple Fiberchannel RAID" - which Sascha
certainly does NOT have. He aims for a SOFTWARE RAID and he wants to
make use of the kernel modules and userspace tools provided with Linux,
not an external box made by Apple.

> On Jan 19, 2006, at 1:50 PM, Sascha Frey wrote:
> 
> > Hi!
> >
> > I'm currently trying to install YDL 4.1 on my G5.
> > I've got two identical disks installed.
> > I want to set up my root partition on a software RAID level 1 array.
> >
> > I leaved /dev/sda1 & /dev/sdb1 untouched (apple partition map). I 
> > created an apple bootstrap aprtition (1 MByte) on every drive 
> > (/dev/sda2 & /dev/sdb2).
> > After this I tried to create a partition with filesystem type Linux 
> > RAID. After setting up size & file system type I get an error message: 
> > "Could not allocate requested partitions: requested FileSystemType 
> > needs a flag that is not available.."
> > I can't create raid partitions.
> >
> > How can I create a software RAID array?
> >
> > I only want to have Linux on this box. Maybe I need to switch to PC 
> > partitioning scheme?

Yes, unfortunately the raid tools provided with Linux expect a PC style
partition table for creating the raid partitions successfully [at least
that was my experience when doing it with a 2.4.22-2g kernel. To change
the partition tables use "parted" - a partition table editor which also
allows you to initialize disks with various styles of partition tables.
It also allows you to set the flags needed for the creation of raid
partitions.

Before doing so, I'd recommend to consult the documentation on TLDP [The
Linux Documentation Project], www.TLDP.org. The documentations there
certainly helped me in getting my raids up and running.
[http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html]
BTW the docs are also available as PDF - so you can read them offline.

> > Partitioning on a Mac seems to be a little bit weired to me...

Not really - keep in mind, that the majority of development for Linux
and its various tools take place on x86 based flavours of Linux.
Therefore most of the documentation silently expects you to have one of
these. This actually does not matter for applications that do not need
access to the hardware directly - which, on the other hand, IS the case
for the kernel RAID modules and therefore it DOES matter.

One thing to think about: I have yet to try booting from a raid partion
on a PPC machine. There is a HOWTO on the LDP site
[http://www.tldp.org/HOWTO/Boot+Root+Raid+LILO.html] - however, yet
again, it is written with x86 arch in mind - I doubt that OF will be
able to load a kernel from a PC style partitioned disk. If anybody can
prove me wrong, please do so - it would only be of help for Sascha.

My solution to this dilemma was to have a small Mac style partitioned
disk [an old 1GB from a dead Mac] to hold boot loader and the /boot
partition to get the kernel loaded. Once the kernel is loaded, it can
recognize the PC style partitions, and your raid schemes can be
recognized as well - and off you go. After that stage, everything is
back to normal.

If anybody out there [maybe YDL themselves] has more detailed experience
on this matter, please share here, or at least point to the appropriate
docs, as this is certainly an important matter for people running
machines that hold valuable data - but lack the funds for HARDWARE
RAIDS.


Sorry for the long post, but I hope this will get you at least closer 
to your goal,

Alex

p.s.: Beste Gruesse und guten Erfolg!

-- 
Alexander Holst
Hergulesse Design
<alex.holst [at] hergulesse [dot] de>