Re: AW: Raid 1 vs 5 ?

[Maarten van den Berg <maarten@vbvb.nl>]

On Friday 07 May 2004 07:52, John Lange wrote:
> Thank you Martin. You have some really great insights there.
>
> A couple of things about the raid sets confused me:
> > Each disk partitioned alike:
> > 	1	30MB
> > 	2	1/2 size_of_swap_
> > 	5	rest_of_disk
> >
> > Now you can create mds on the disk:
> > 	md0	raid1 sda1 sda2 sda3 sda4
> > 	md1	raid1 sda1 sdb1
> > 	md2	raid1 sdc1 sdd1
> > 	md3	raid5 sda5 sdb5 sdc5 sdd5
>
> First, why do we skip sdx3 and sdx4 on each disk and go directly to sdx5
> for partition numbers?

That is the first number a logical partition gets, as opposed to primary.

> Second, I'm very confused by the way you divided up the raid sets....
> I'm thinking you erred? I'm such a newb its possible I really don't
> understand whats going on so hopefully you can verify.

I concur, there are errors. This is probably what he meant

> md0: did you mean sda1 sdb1 sdc1 sdd1 ?

Yes. It was obviously a typo.

> md1: did you mean sda2 sdb2 ?
> md2: did you mean sdc2 sdd2 ?

If it were me, why not do entire swap (not 1/2 size_of_swap) on a four-way 
raid 1, just as with /boot ?  Is way simpler.

> md3: did you mean sda5 sdb5 sdc5 sdd5 ?
>
> And last, is it possible to build the system from the beginning on RAID?
> I'm using slackware. I see there is a section in the how-to for
> converting a red hat system after the fact but obviously it would be
> easier if I didn't have to do that.

What proved the easiest for me is installing the OS on a temporary scrap 
harddisk, build your raid sets from there on the real target disks and copy.
There is a more complicated way too, it involves setting failed-disk status on 
the drive holding your original data. 

Maarten