Re: RAID: identical disks?

On Wed, 30 Nov 2005 07:37:24 +1100, "Rod Speed" <rod_speed@xxxxxxxxx>
wrote:

>Curious George <cg@xxxxxxxxx> wrote
>> Rod Speed rod_speed@xxxxxxxxx wrote
>>> Curious George <cg@xxxxxxxxx> wrote
>>>> 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.
>
>>>> When disks are mismatched the best case scenario is performance,
>>>> space, firmware optimizations are limited by the lesser drive. In a
>>>> worst case scenario it causes compatibility problems. Fortunately
>>>> on modern hardware esp with software or firmware assisted
>>>> software raid this worst case scenario is virtually a non-issue.
>
>>>>> 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.
>
>>>>> 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.
>
>>>> There is most definitely a U-shaped or bathtub curve to hardware
>>>> failure over time. However both drives in a 2 drive array dying
>>>> natural deaths within hours of another is quite unlikely.
>
>>> Not if the system is out of spec, too hot or a bad power supply.
>
>> that wouldn't be a "natural death" now would it
>
>The original wasnt about "natural death", it was clearly
>about what gives the best result, regardless of what
>happens. It aint just about handling hard drive failure
>gracefully, its also about handling other failures
>gracefully too if that can be done essentially for free
>by using two different drives instead of two identicals.

clueless, nonsensical back peddling

>>>> Rather than mixing models some ppl buy parts from
>>>> different suppliers to hedge their bets or simply count
>>>> on premature failure to introduce media of different
>>>> ages or simply proactively decommission arrays at
>>>> the end of expected service life rather than wait for
>>>> the catastrophic event.
>
>>> Or just use two quite different models that are compatible.
>
>> offering an alternative is not saying "you can't."
>
>Never said you did, I just pointed out the advantage of that approach.

no you didn't. No advantage has been pointed out. You're simply
insisting on that method.
.