[Gllug] pata software Raid

[Peter Ball]

Hi

On 9 Aug 2007 at 17:15, Ziya Suzen wrote:

> On 8/9/07, Peter Ball <CFL at marguet-ball.net> wrote:

> > The Software-RAID-HOWTO gives very good reasons why not to put 2 ide
> > disks on the same bus.
> >
> > However is there any reason why you shouldn't put a cd or dvd as a
> > secondary on one of the buses ?
> 
> Well, wouldn't it be kind of the same reason? If your CD drive fails
> it would take the HDD down with it, adding to the risk of failures?! I
> am not 100% sure but that's how I understand it. I am about to setup a
> software raid as well, so I am interested in the subject too.

I'm not sure that the failure reason is so pressing.  The suggestion in the Raid How To is 
that if the master hd fails this confuses both the controller chip and  the secondary hd on the 
same bus.  This could leave you with a dead master hd and a corrupt secondary hd and 
thus a dead and un-recoverable raid 5 array.

With a master hd and secondary cd/dvd on the same bus the worst that can happen (on this 
bus) is that you loose 1 hard disk - that's what raid 5 is designed for.  In reality the risk that 
the cd/dvd fails is probably very slight and that a secondary failure is less likely to bring the 
bus down.  I see hd failures on a regular basis, I hardly ever see cd/dvd failures and those 
very few that I have seen have been down to user clumsiness.  This drive is going to be 
used for an initial install (several times till I get it the way I want it), possibly upgrades and 
possibly for an emergency boot cd.

Assuming that my logic is correct the thing that interests me is whether the cd/dvd will slow 
the bus down for the hd.

-----------------------------------
Peter Ball
Computers For Linguists
peter.ball at marguet-ball.net
Tel:    +44(0)20 7732 1741
Fax:    +44(0)20 7358 9214
Mobile: +44(0)77 1968 2913
45 Endwell Road, London, SE4 2PQ, United Kingdom

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