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     áòèé÷ :: Filmscanners
Filmscanners mailing list archive (filmscanners@halftone.co.uk)

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RE: filmscanners: Best solution for HD and images



> Thus in the case of SCSI where you cannot (by definition) overcome the
> number of 6 devices x chain/controller,

WHAT SCSI are you talking about?  Try 16. not 6.

> BTW , this method compulsorily implies a DOUBLE WRITING need i.e.
> write the
> data + write the new parity (even if on another disk) and this is
> meaning a
> LOSS OF SPEED/EFFICIENCY (relatively to the achievable speed/efficiency of
> the disks)

That's not true.  There is no "double write", both the data/parity is
written at the same time.  Parity can easily be calculated on the fly.

> Yesterday night I have bought on eBay an IBM U-160 10000rpm 18GB new and
> under warranty for 102 USD + 20$ of shipment to Italy from USA
> and this unit
> will be the fourth inside my system while having 2 x CD/R (IDE)
> and 1 x DVD
> (IDE) .
> My aggregated sustained transfer rate is 3 x 35MB/s + 1 x 29MB/s
> = 134MB/s =

The data rate doesn't just "aggregate" like that.  There is SCSI overhead
that decreases the effective overall transfer rate.  Not all files are
sequential, and without spindle locking, there is quite a bit of latency.
Run some benchmarks on your system and see for your self.  Also, make sure
the benchmarks AREN'T running out of disk cache...that hardly tests the disk
speed.  You'll be lucky to get even near 80, if even 60.

> the limit of a 32bit PCI bus at 133MHz (but still in the limits of an
> Adaptec 29160 controller)

The standard PCI bus is 33 MHz (or 66MHz), NOT 133MHz.  Perhaps you mean
132M BYTES/sec?  Even at that, you can't get near %80 of that, if you're
lucky.  132M bytes/sec is the burst rate.  There is substantial overhead on
the PCI bus that lowers that substantially.




 




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