I have not seen an answer to the AutoRAID part of this question yet. Lots of
answers for MPE/iX in general. But most of the answers seem to revolve
around how fragmented data ends up on the disc drive physically.

With RAID 0/1 (or RAID 5 for that matter), one has logical drives which have
little or no relation to the physical drives. Data is "banded'. In other
words it is spread over all the physical spindles. Even the smallest
read/write request is likely to access most of the physical disc drives.

So I do not see how fragmentation can possibly change the physical
performance of an AutoRAID at all. If there is any performance degradation
left with having fragmented discs under MPE/iX and an AutoRAID, is it due to
something like memory paging? Or something else? Or is my thinking about how
RAID works wrong?

Thanks,
Timothy Atwood
Holtenwood Computing
http://www.holtenwood.bc.ca/computing/
for Domtar Vancouver Mill
(Opinions expressed are mine and do not reflect Domtar)

>  -----Original Message-----
> From:         Atwood, Tim (DVM)
> Sent: Monday, October 21, 2002 12:49 PM
> To:   HP3000-L (E-mail)
> Subject:      How Important Defragmenting Discs on HP3000 with AutoRAID
>
> In old classic days we used to defragment our disc drives religiously.
> With the changes in file structure for MPE/iX we seem to have needed it a
> lot less often.
>
> Fairly recently we converted to an AutoRAID 12H for discs. The AutoRAID
> spreads data physically across the spindles anyway, so I do not see how a
> fragmented disc makes much difference to the physical file structure. Also
> the new 12H has enough storage space that I doubt we will run out of large
> contiguous chunks of logical disc space for years to come.
>
> So what do people think? Does it make sense to waste resources
> defragmenting the disc under these conditions?
>
> MPE 6.0 PP2
> AutoRAID 12H
>

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