Ron,
Well, there is no mistaking this feedback ;-)
Thanks for the direct, succinct feedback. I think you are right in your
points.
The search goes on to balance flexibility, cost, and benefits, as
always.
Erik.
> -----Original Message-----
> From: linux-lvm-bounces@redhat.com
> [mailto:linux-lvm-bounces@redhat.com] On Behalf Of Ron Watkins
> Sent: Tuesday, March 01, 2005 11:10 PM
> To: Erik@echohome.org; LVM general discussion and development
> Subject: Re: Building up a RAID5 LVM home server (long)
>
>
> This is absolutely insane. It is among the dumbest designs
> I've ever seen.
> You are using HDA as a component in MD0 and MD1, and then
> using HDA AGAIN as
> part of MD2 directly, while using it indirectly via MD0 and
> MD1. You're
> going to A) bottleneck on HDA, B) you're going to beat that
> drive to death,
> and C) if that drive goes, you are HOSED. Plus, you are just
> begging for
> problems with potential bugs in the RAID driver code. This
> whole setup is
> an INCREDIBLY bad idea. You're trying to 'be clever' to save
> yourself some
> money, and all you're doing is buying trouble.
>
> The way RAID5 is meant to work is with disks of approximately
> the same size.
> RAID5 is not expandable, unless you have a very expensive hardware
> controller. There are algorithms that will let you expand
> the size of a
> RAID5 volume, but they have not, to my knowledge, been
> implemented in open
> source. You CANNOT do what you want to do, cheaply. You
> can spend a great
> deal of money to satisfy most of your design parameters, but
> NOT cheaply.
> If you want it cheap, use fixed drives of about the same
> size, and don't
> think about expansion. When you're ready to expand, hook up
> another, bigger
> RAID and copy your data. In NO case can you use that
> hodgepodge of junk
> drives you've collected.
>
> Most of your drives are obsolete. Keep the biggest one, buy
> at least two
> more of the same size, and set up a RAID5 using that. All
> this monkeying
> around to try to extract some last value from drives totally
> ill-suited for
> the purpose is going to cost you far, far more than new
> drives ever could.
>
> Hell, keep the smaller ones around, put them into a concatenated LVM2
> volume, and use them as a backup. It's not the best backup
> in the world,
> but it's better than nothing.
>
> Do it right. This is your data you're trying to save. You
> can get very
> nice 250-gig PATA Western Digital drives for $165 from
> www.newegg.com. They
> are specifically designed for RAID. Buy 4 and save yourself
> this massive
> headache. If you don't need that much space, buy smaller drives.
>
> Or, you can persist in trying to be clever, but it's a
> virtual *certainty*
> you're going to lose data if you go this route. Pay now, or
> pay later.
> What's your data worth?
>
> <<RON>>
>
> ----- Original Message -----
> From: "Erik Ohrnberger" <erik@echohome.org>
> To: "'LVM general discussion and development'" <linux-lvm@redhat.com>
> Sent: Tuesday, March 01, 2005 10:27 PM
> Subject: RE: Building up a RAID5 LVM home server (long)
>
>
> >
> > ... SNIP ...
> >> >What if the I broke everything into 10 GB pieces, and
> >> created multiple
> >> >raid5 sets? Then I could LVM2 them together and have a large
> >> >filesystem that way.
> >> >
> >> >a=20GB, b=30GB, c=40GB
> >> >
> >> >a-1 + b-1 + c-1 = md0 (approx 30 GB storage)
> >> >a-2 + b-2 + c-2 = md1 (approx 30 GB storage)
> >> > b-3 + c-3 = md2 (waiting for one more drive)
> >> > c-4 = md3 (waiting for two more drives)
> >> >
> >> >
> >> This is sorta what I do. But in my opinion the gain of
> having RAID5
> >> (over RAID1) is when you get over 3 disks... at 3 disks you are
> >> burning 33% for redudnacy... 25% or 20% or 17% sounds
> better to me.
> >> I guess if
> >> you go too far it costs in calculating the parity.
> >
> > Overhead: Yea, OK. Nothing is without a price.
> > I fooled around with various ideas, and came up with this for my
> > particulars:
> > (Note, rounded to nearest GB)
> >
> > 80 GB /dev/hda 60 GB /dev/hdb 40 GB /dev/hdc 45 GB
> > /dev/hdd
> >
> > GB /dev/md0 (RAID0)
> > 40 /dev/hdc
> > 15 /dev/hda1
> > 55
> >
> > /dev/md1 (RAID0)
> > 45 /dev/hdd
> > 10 /dev/hda2
> > 55
> >
> > /dev/md2 (RAID5)
> > 55 /dev/md0
> > 55 /dev/md1
> > 55 /dev/hda3
> > 55 /dev/hdb
> > 220
> >
> > Yea, OK, so like the 220 is a bit optimistic, but should get pretty
> > close
> > to
> > that.
> >
> > What do you think?
> >
> >
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-> lvm
> > read the
> LVM HOW-TO at
> http://tldp.org/HOWTO/LVM-HOWTO/
> >
>
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