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To: gentoo-amd64@g.o
From: Duncan <1i5t5.duncan@...>
Subject: Re: Re: Root on Raid and LVM
Date: Wed, 02 Nov 2005 15:12:36 -0700
Florian D. posted <4368B219.1070903@...>, excerpted below,  on Wed, 02
Nov 2005 13:33:29 +0100:

>> ...  As some may guess, I've been studying this stuff recently!  =8^)  I
>> don't have my own RAID setup yet, but probably will by late this week.  (I
>> plan to go pickup the drives probably Tue or Wed.)
> good luck. when there is no email from you for some days, then we know 
> sth. went wrong ;-)

=8^)  I have the drives... four Seagate SATA 300 gigs.  I got them
yesterday and installed them this AM.  I haven't done anything with them
yet, so they're just empty unconfigured drives still, but the BIOS and
kernel see them, so I've gotten a good start!  =8^)

I've now got this full tower case stuffed to the gills! =8^)  The four
SATA drives, my current main drive, a 250 gig Maxtor PATA, on PATA primary
master, a DVD writer on PATA primary slave, an old 36 gig Maxtor on PATA
secondary master, and a CD writer on PATA secondary slave.  Round that out
with a legacy 3.5" floppy, and I've got 9 drives in this thing, with > 1.4
TB of hard drive capacity (pre-raid mirror/parity discounting)!

The 250 gig still has  ~100 gig not even formatted yet, but my AC went out
this summer and it got hot and developed some bad blocks.  With them all
marked and one 4 gig partition written off entirely, it has proved
decently stable, but I've been worried about it, thus the current upgrade
job.  I've been considering RAID and drives are now cheap enough to do it,
so I decided to go for it!

I'll be setting up three RAID sets on the four SATAs, and will be using
the Maxtors as emergency boot and backups.  A small 4-way raid1 will have
/boot.  The majority of the disks, 200+ gig of each of the four, will be a
raid6 (raid5 but with two parity copies... any two drives can go down, one
out is supposed to maintain speed fairly well, two out will drop speed
substantially but will still function) carrying root, /usr, /var, /home,
and my dedicated mail, news, and media LVs.  A medium size raid0
will complete the roundup, containing /tmp (which is $PORTAGE_TMPDIR) and
a dedicated ccache LV.  I'm currently running 1G memory and no swap, but 
I think I'll reactivate swap as well while I'm at it, with a small
non-raid swap partition on each of the four.  The kernel stripes swap on
its own, so there's little reason for me to put it on raid, and one of
the reasons I'm reactivating swap is to try out the developing kernel SMP
suspend features. =8^)  Having swap on raid isn't likely to work too well,
when I'm trying to load memory images out of swap coming out of suspend!

I'll use my existing Maxtor PATAs, as I said, for an emergency boot
installation and off-RAID online backups, and plan on using LVM2's
snapshotting capacities to maintain probably up to two working snapshots
(yes, I'm aware of the write penalty of doing so) of root and /usr, taken
before any major upgrades, such as to a new baselayout or a new version of
KDE. Once I verify functionality of the new upgrades, I'll make
necessary config changes (like switching fstabs), then write off the
snapshot to the non-raid emergency backup, so I can remove it and avoid
the write penalty of the COW (copy on write) snapshot.

Currently, I have a working copy and a backup copy of both root and /usr
on each of my Maxtors, therefore, four OS area snapshots total.  That has
proven to be a good strategy, when I got those badblocks due to the bad
A/C and consequent overheating, but after having used it, I decided it
needed a bit of modification, mainly in that I needed a better way to keep
the snapshots updated so they didn't get massively outdated.  The RAID
gives me better reliability on the one side (and the Seagates with their 5
year warrantee are nice in that department as well), and lvm2's
snapshotting should come in handy as an intermediate stage from the other
angle.

As I mentioned, I still have ~100 gig unpartitioned on the 250 gig.  I'll
maintain that practice on the raid, but the dynamic expansion capabilities
of lvm2 will provide significant additional flexibility in that area.

Well, I've got a quite a bit of work to do still, soo...

-- 
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


-- 
gentoo-amd64@g.o mailing list


References:
Root on Raid and LVM
-- Chris S
Re: Root on Raid and LVM
-- Chris Smart
Re: Root on Raid and LVM
-- Florian D.
Re: Root on Raid and LVM
-- Duncan
Re: Re: Root on Raid and LVM
-- Florian D.
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