Re: Draft Mirrored Linux Mini How-to

["Keld Jørn Simonsen" <keld@dkuug.dk>]

Forgot to cc linux-raid...

keld

On Fri, Aug 07, 2009 at 07:34:23PM +0200, Keld Jørn Simonsen wrote:
> On Fri, Aug 07, 2009 at 12:52:34PM -0400, Harold Pritchett wrote:
> > Keld Jørn Simonsen wrote:
> >
> >> It is a good idea to have a how-to. But there are already a few around.
> >> I wrote something like it for our wiki at
> >> http://linux-raid.osdl.org/index.php/Preventing_against_a_failing_disk
> >> but with some more advanced features, such as you do not crash if one
> >> disk fails, and you can reboot the system without a rescue disk, and you
> >> get faster mirrored raid, avoiding the slow raid 1. It does not do LVM,
> >> however, and I think that how-to should be enhanced with LVM.
> >
> > I guess this would depend upon the linux.  Currently, I am working with
> > Centos 5.3 and the only raid personalities available in the kernel on
> > the DVD appear to be RAID0, RAID1, RAID5, and RAID6.  With two disks
> > this limits us to RAID0 and RAID1.
> 
> I am also running centos 5.3 and raid10 is supported, and I run most of
> my data on it.
> 
> >>> I'm from the old school.  I believe in lots of partitions.  Create any
> >>> additional partitions you may need.  If you really want to, you can
> >>> just create a single partition and put "/" in it.  You still will
> >>> need the "/boot" partition since you can't boot from an LVM partition.
> >>
> >> I think it is good to have a / , a /home, and possibly a /boot 
> >> partition, but having more partitions is probably just shooting 
> >> yourself in the
> >> foot, because you may create space problems. Those smaill partitions can
> >> easily hit some roof, like /var (when logs run full)  and /tmp (doing temporary
> >> work like editing in big files), /opt and /usr/local (installing big new packages)
> >> and why should /usr and / be on different partition - that beats me.
> >
> > As I said, I'm from the old school originally cutting my teeth on BSD unix in
> > the 1980's.  In those days, disks were always too small.  A couple of 20 MB
> > disks (that's MB, not GB) was a LOT of space back then.  By using multiple
> > partitions you could keep a run-away from crashing the whole system when it
> > filled up /tmp or /var.
> 
> I am also from that time, starting out with UNIX V6 on RL05 with 2.5 MB on a PDP-11/45.
> And we had a *big* 40 MB disk in the corner. Later we ran VAX'en and BSD
> 4.2 - still I think it is better to keep the system things in one
> partition. Anyway why not describe both, and tell of pros and cons.
> 
> > But once again, this personal preferences.  All you really need is /boot, / and
> > some swap space.
> 
> I agree with that.
> 
> >>> You can now continue to install linux normally.  I usually do it twice.
> >>> the first time is to get an idea of how big each partition should be
> >>> and the second time is to get it right.
> >>
> >> That is cumbersome, and probably caused by your use of many partitions.
> >> It will turn some novices off.
> >
> > Make the default a single partition and put the multiple partition version in an
> > appendix...  In today's world of TeraByte disk drives for under $100.00 It may
> > be the best idea to just put it all in a single file system.
> 
> as sad you could decribe both. For pedagogical reasons, and because it
> does not matter very much, you could probebly benefit from describing
> the simpler version.
> 
> >> why can't you boot from the working drive?
> >> The system should be configured to do this.
> >>
> >>> 4.  Boot from the linux rescue CD/DVD and start the system, no network.
> >>
> >> better avoid the rescue cd by making the system bootable from both drives.'
> >
> > can do...  I just didn't think of this...
> >
> >>> 14. Wait for the mirror to sync.  It may take several hours
> >>
> >> you can begin using the system immediately, while the raids are syncing.
> >
> > Good point.  I knew that and just didn't say it.
> >
> >> it would be nice if you could reference our wiki, wherever you put up
> >> your howto.
> >
> > I would be glad to...  In fact, if we get something useful, you might want
> > to put a copy on the wiki...
> 
> to me it is very overlapping with what is already up there.
> For now I cannot see the benefit of two howtos with the same aim.
> Better consolidate it.
> 
> best regards
> keld
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