Raid 1+0

[Lowell Gilbert]

"Valeri Galtsev" <galtsev at kicp.uchicago.edu> writes:

> On Tue, April 19, 2016 9:38 am, Steve O'Hara-Smith wrote:
>> On Mon, 18 Apr 2016 17:05:22 -0500 (CDT)
>> "Valeri Galtsev" <galtsev at kicp.uchicago.edu> wrote:
>>
>>> Not correct. First of all, in most of the cases, failure of each of the
>>> drives are independent events
>>
>> 	If only that were so. When the drives are as near identical as
>> manufacturing can make them and have had very similar histories they
>> can be expected to have very similar wear and be similarly close to
>> failure at all times, which makes it likely that the load imposed by
>> one failing will push another over.
>
> Sigh. You need suggest some physics that will make one drive affect
> another (aged or not aged doesn't matter for me). Then you will have me in
> your team.

Correlation is not causation.

It's not a big stretch to imagine that two nearly identical mechanical
devices, operated in nearly identical conditions, might wear out in a
nearly identical way at about the same time. There is no need for one
drive to affect the other.

A fair number of people believe that this in fact occurs. I've looked
for evidence on the subject, and I haven't found anything (beyond
anecdotes) for or against the possibility.