[rescue] Small RAID array setup

Phil Stracchino alaric at caerllewys.net
Fri Jun 27 12:21:14 CDT 2003

On Fri, Jun 27, 2003 at 09:59:20AM -0400, Andrew Weiss wrote:
> I had an idea a bit ago... why not just RAID disks...
> New HD's with two spindles in the drive that counter-rotate *(like the 
> original drives from the 60's)
> The spindles mesh together... i.e. one platter on one... then platter 
> on the other... then back
> ----
>   -----
> ----
>    ----
> and the rw heads are on the sides of the drive... one on each 
> intersection
>    |
> OO
>    |
> indicated by the pipe position.
> This drive can either be configured for fast access as one stripe or 
> redundancy via internal mirroring.
> Then you can stripe this set of mirrors and be done with things.

The mechanical complexity boggles the mind, and I see no advantage that
it offers over a single spindle.  Have you considered:

(1) You now need two separate spindle motors?
(2) You gain nothing in access speed unless you have two controller
    boards driving two separate steppers?
(3) Disk heads "fly" on the boundary-layer airstream, and need a clean
    boundary layer do to it.  Have you considered the turbulence greated
    by two platters spinning in opposite directions at 10000rpm a few
    millimeters apart?
(4) Internal mirroring like this would be utterly pointless.  If one
    half of the drive loses power, so does the other.  If one half has a
    head crash, it's GOING to take the other half with it, guaranteed.
(5) This scheme would be less reliable than a single disk, because
    there's twice as many moving mechanical assemblies to fail (at a
    first approximation), but you still have to swap out the entire disk
    if one half fails.
(6) Increased size, increased power dissipation, increased heat,
    increased noise, increased cost ....

I could go on, but I think that's quite enough.

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