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To: gentoo-desktop@g.o
From: Duncan <1i5t5.duncan@...>
Subject: Re: disk partitioning
Date: Wed, 7 Feb 2007 10:34:34 +0000 (UTC)
Kevin Hanson <tuxpert@...> posted 45C92BFC.2020503@...,
excerpted below, on  Tue, 06 Feb 2007 19:31:40 -0600:

>> Did you look in to EVMS at all.  I am setting up a similar system to 
>> yours...4 stat disk, linux raid, etc.  However, I really wanted to use 
>> EVMS and am only partially successful.  I have, as of now, been able 
>> to get the EVMS stuff correctly in initrd such that I can complete a 
>> boot.
>>
>> Just curious if you'd looked into EVMS at all and if you had any 
>> thoughts.

> Wow...I didn't type well in the above message...it's supposed to be 
> 'sata' not 'stat' disk...
> And I was trying to say "I have, as of now, NOT been able...."

It seems to be going around. =8^(

[I'm adding this after typing the below.  It occurs to me I might be
discussing everything /except/ what you need.  If so, I'm sorry.  I'm
posting this however, in case it can do /someone/ some good, even if
that's not you.  Hopefully it helps you too, but if not, after putting all
this effort into it, I hope it helps /someone/. =8^) ]

I haven't looked into EVMS, no.  However, as I understand it, while EVMS
and LVM2 were at one time built on different kernel mechanisms, when LVM2
was selected for merging into the mainline kernel (2.5 era I believe,
2002), EVMS decided rather than fight it, to take their already great
management tools and make them work with the LVM2 framework as it was
merged into the kernel. =8^)  Thus, I believe EVMS is now simply what
amounts to a GUI front-end to the LVM2 system as it exists in the kernel
and lower level command-line tools.

If it's not working for you, presumably the issue is that something isn't
configured right in the lower level LVM2 layer.  Sometimes you just gotta
dive in and get your hands dirty at the command line level to most
efficiently figure out what's going wrong, and this would appear to be one
of those times.  You may or may not eventually figure out the issue at the
higher level, but once you understand what's going on at the lower level
and fix the problem, I'm guessing you should be able to go right back to
using your higher level interface for routine work, if so desired.

My approach was to take one thing at a time.  First I studied RAID and
mdadm and got how it worked figured out at least enough to design the
system I wanted at that level.  Then I did the same with LVM2.  Honestly,
I was aware of the EVMS thing, but had forgotten the details, and it never
occurred to me to try it since I was under the impression that they had
lost out (they did with their lower layers, but just took their strengths,
the upper layers, and refitted them to the LVM2 framework, actually a
rather cool thing to do IMO) and were no longer a mainline Linux project
(I was wrong there, since they continued with their GUI front-end, just
built on LVM).

Actually, I had another thing to learn as well.  When I started on Linux
using Mandrake, GRUB was far less mature and I learned LILO.  When I
transferred to Gentoo, I just continued using LILO, for awhile just using
the Mandrake executable on Gentoo, even.  Since I was setting up an
entirely new RAID system anyway, and already learning it and LVM2, I
decided it was time to bite the bullet and learn and switch to GRUB as
well, so I learned it too. =8^)

Then after I actually got an overview of how it all fit together, and had
designed my system at that level so I could actually start working with
it, I retraced the same steps only this time actually getting the
operational detail and putting it into practice as I went.  Partitioned
RAID in particular, however, never /was/ entirely clear to me, until I
started actually doing it.  That was mainly because it was new enough that
there were tantalizing mentions of it, but not the direct coverage of
every aspect of it, both theory and step-by-step, that I was able to get
with RAID and LVM2 in general, using mainly the three sources of each ones
HOWTO, together with the Gentoo LVM and RAID documentation.

Since I already knew I didn't want LVM2 on my root partitions, because
that would require the additional complexity of an initramfs and I wanted
to retain direct-kernel-boot, I was able to (1) do the physical drive
partitioning (no problem, I'd done that many times over the years), (2)
create and assemble the RAID-1 for /boot, (3) while still booting from my
separate single drive (legacy PATA), play with that until I got the
practical knowledge of how to actually get the kernel to see and assemble
the RAID, (4) while still booting from the separate disk, figure out how
to mkfs the assembled RAID-1, (5) still booting from the separate disk,
install the kernel and grub to the new RAID-1, (6) still booting the
separate disk, figure out how to get GRUB installed on the physical boot
sectors of ALL FOUR physical disks, (7) NOW figure out how to actually
boot grub from any of the four, and verify that it actually worked as I
intended, (8) get the GRUB config and kernel command line correct to
actually get from GRUB into a kernel installed on that RAID-1 /boot. (9)
NOW with the RAID-1 working and actually booting to the root on my
existing single drive, figure out the partitioned RAID-6 for the root
filesystems and LVM2 partition (this started to get easier since now I
only had to learn the difference between RAID-1 and RAID-6, and between
partitioned and non-partitioned RAID, I already had practical knowledge of
working with RAID in general using mdadm), (10) verify that there were
indeed no weird tricks to partitioned RAID I hadn't considered, and
actually partition the RAID-6 using cfdisk, (11) not yet quite believing
it could actually be this simple (but it was), since this hadn't been
covered so well in the documentation since partitioned RAID was so new,
mkfs the partitioned RAID-6 partitions, (12) mirror my existing root file
system off the legacy PATA drive onto the two RAID-6 root partitions, once
to each, working and backup, (13) figure out how to get GRUB to point the
kernel at these new partitions for its root, (14) actually boot into the
new partitions and see that everything so far was working.

Only at THAT point did I even START to consider the practical knowledge of
the LVM2 stuff.  At that point, I had verified working partitioned RAID-6,
as I was booting into it as my root filesystem, so I knew at least to that
point, everything HAD to be working, since I'd not be able to boot into it
if not!  Again, the lower complexity of the partitioned RAID for my root
filesystems paid off, as I was able to learn, create, and test the
individual components to that point, before I even /began/ worrying about
how LVM2 fit into all of this.

Since I knew I had a basically working RAID system by then, not only was I
able to learn and test LVM2 as an entirely separate from the actual
boot kernel and the RAID component, but I was under MUCH less stress while
doing so, since even if LVM2 didn't work at that point, I knew I could
simply fall back to the old partitioning methods I knew so well, and that
it couldn't be an issue keeping me from completing setup of a working
system.  Under those conditions, I reviewed the LVM2 HOWTO I had studied
earlier in ordered to figure out how to actually design the thing I had in
mind, this time actually doing the physical setup in practice.  Again, by
this time it was surprisingly easy, as it was just one more layer added to
a system I already knew was working, and the HOWTO and Gentoo
documentation, both at the Gentoo site and in the sample config file as
merged, was actually quite good and very clear.

So... if you are having problems, contrasting your approach with mine, I'd
have a couple suggestions.  (1) Get the EVMS layer out of the way until
you actually get the LVM2 layer beneath it working, groking the LVM2 layer
better as you go as an added benefit.  (2)  Even if it's temporary, just
to familiarize yourself with how things actually work, consider breaking
down the components as I did, separating the RAID from the LVM2, and
learning one at a time.  Once you know your RAID is working and are
at least working comfortable with mdadm or raidtools, /then/ add in the
LVM2 layer.  Once you are comfortable working with it as a component at
that level, either add in the initramfs aspect or the EVMS aspect, but not
both at once, and get comfortable working with it.  Then and only then,
throw in the other, completing the system the way you originally intended.

It may also help to get familiar with initramfs on its own, quite apart
from the whole RAID/LVM2/EVMS thing.  However you are running now, try it
there and figure out how the whole initramfs thing works at least to the
level you can be fairly confident of tracking down the problem to it if
that's where it is, before you worry about the other stuff.  That way, you
can throw that knowledge you already have into the RAID/LVM2/EVMS mix at
the proper time.  Of course, if you do this, you'll have already gone
where I've not yet tread, since I do NOT have that practical level of
knowledge of how initramfs actually works, altho I've read enough to know
a bit of the theory.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

-- 
gentoo-desktop@g.o mailing list


Replies:
Re: Re: disk partitioning
-- Lindsay Haisley
References:
disk partitioning
-- Mikko Husari
Re: disk partitioning
-- Duncan
Re: Re: disk partitioning
-- Kevin Hanson
Re: Re: disk partitioning
-- Kevin Hanson
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