[gentoo-amd64] Re: Root on Raid and LVM - Solved

[Duncan <1i5t5.duncan@cox.net>]

Edward Middleton posted <4368286D.90909@nikon-sys.co.jp>, excerpted below,
 on Wed, 02 Nov 2005 11:46:05 +0900:

>>It appears most aren't running into this bug, yet the number of bugs
>>suggests there's a fair number of users.
> This bug will only effect users of root on lvm2 users

BTW, I'm not fully up and working yet, but I've decided to put root
directly on (a partitioned) raid6, so it can be directly auto-assembled by
the kernel and I won't have to use an initrd/initramfs, as (I believe??) I
would if root was on LVM2.  (The software raid howto is outdated when it
says Linux raid can't be partitioned.  The 2.6 kernel handles that just
fine, but with different device numbers than the traditional
non-partitionable raid.)

I got 4-300 gig Seagates -- 1.2 terabyte of raw disk space (plus my
existing PATA drive space).  One of the reasons I'm not up and running yet
is that I double-checked the raw drives by running badblocks -w on each
entire drive.  That's four patterns, written out one at a time to four
drives, 300 gig each, then read back in and verified.  4x4x300 gig = 4.8
terabytes written, 4.8 terabytes read.  That took me a couple days!  =8^)
Fortunately, I didn't feel it much at all, save for the wait, because that
was traffic on drives I'm not yet using in production, and while it did
run 1 CPU to 100% for the entire period, that was mostly I/O wait, and my
other CPU kept up with the normal desktop stuff just fine.  Anyway... it
was waiting for that, that I realized just how much drive space I now
have! =8^)

I have the raid6 partitioned three ways, my traditional root and
backup-root-snapshot as two partitions with the third being the big one --
to hold the rest of my raid6 volumes in LVM, again, for the additional
flexibility.  There's enough space on the LVM-on-raid6 partition to keep a
working and a snapshot copy of everything there, too, guarding against
fat-fingering as well as hard drive failure.  (A second copy of everything
means very little risk playing with reiser4 or the like, as well! =8^)

Right now, I have three raids set up (altho I haven't installed
filesystems on them yet), a small raid0 (mirrored) for booting, the
majority of the space as the three-way-partitioned raid6 mentioned above,
and a raid0 (striped for speed, non-redundant) for semi-volatile storage,
the portage tree as it can easily be resynced for recovery, /tmp, etc (no,
not /etc! <g>).  However, after reading up on LVM and realizing it had
built-in striping capabilities, I may kill the raid0 and simply use
striped LVM directly on the physical volume partitions underneath.

Anyway... it was quite cool to realize the 2.6 kernel handles partitioned
raid, now, and with direct boot-time kernel raid assembly, I could run
root on raid6 without an initrd/initramfs!  As I was dreading the
complexity of an initrd solution, I grabbed the opportunity to avoid it
and still have a raid-backed root, when I saw it!  So, no root on LVM
here!

-- 
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 in
http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html


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