Re: RAID: identical disks?

In comp.sys.ibm.pc.hardware.storage J. Clarke <jclarke.usenet@xxxxxxxxxxxxxxxx> wrote:
> void@xxxxxxxxxxx wrote:

>> I've read that it's best to set up RAID with identical disks (same brand
>> and
>> model). I've got a Samsung SP1213N hard drive which I got 21 months ago,
>> and
>> now I want to set up RAID 1 on my machine. So I'll need to get another
>> Samsung SP1213N. But I know that sometimes manufacturers will make slight
>> changes to hardware and still keep the same model number. I don't know if
>> Samsung has done anything to this particular drive in the 21 months since
>> I bought mine, so hopefully buying a recent one will be OK to set up a
>> RAID mirror.

> In practice, as long as the secondary is of the same capacity or
> higher than the primary, and of about the same performance, a RAID1
> will work fine.

Why that? Do you assume array creation only with the primay disk
connected? Or is some RAID software too stupid to recognize which
disk is the smaller one?

> In fact there is a school of thought that the two disks should be
> _different_ brands and/or models on the theory that if they are they
> same they might be so closely matched that they both might fail at
> the same time or close enough to it that you don't have time to
> rebuild the mirror.

This sure makes sense if both disks have a shared weakness, e.g.
extreme sensitivity to heat, power-spikes, shock or the like.
I find it overly paranoid for everyday use, but especially in
a machine you cannot easily get to this makes sense. There you
might even consider using 3 or more different disks in RAID1
array.

> Having seen four Japanese-made light bulbs installed at the same
> time fail within four hours of each other a year and a half later, I
> am not going to denigrate this notion, although I don't consider
> such failure to be exceedingly likely.

Pretty unlikely without a common factor. Maybe overvoltage or
mechanical shock?

Arno

.

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