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Re: DPS Quatrus board with Huge U320

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Michael AndersonRe: DPS Quatrus board with Huge U320
by on Dec 13, 2003 at 7:18:23 pm

Hi Andrei,

I apologize in advance for my long winded answer:

First, yes, this is a single 5 drive U320 unit that is hardware striped and appears as one drive to the Quattrus.

Concerning "saturating" the U160 bus with two units, here's what I've seen:

The Quattrus generates very nice IOs. They appear to be a field size (about 300k), with little or no variation. When a timeline is started, the Quattrus prefetches it's own internal buffers, then generates IOs for each stream as it needs it. This appears as "semi-random" IOs to the storage device, though in fact they are multi-stream sequential.

For recording data, the Quattrus negotiates an 80MB/second data rate. For playing data, it negotiates a 160MB/second data rate. This is the rate of the data when it's actually moving. To compute the available data rate, you have to take a ratio of the time data is moving divided by the total "wall clock" time, which includes BUS FREE phases, Artibration, Selection, Command and Status phases. Hence the total theoretical rate is some large fraction of 160MB/Second. In my analysis, both the Cheeta drives and our drives have a net "potential" rate of about 100MB/Second.

So from what I've seen, playing 4 streams of uncompressed video achieves about 80% of the total available data rate (80MB/Second produced divided by 100MB/Second available). My guess is adding another unit will only provide a margin performance improvement. I.E., the bus is almost saturated with a single unit.

To be totally fair, the Cheeta drives are a little more effecient on the bus than the Huge disk array, so their total available data rate may be higher. However, the Huge disk array generates almost 300MB/Second internally to a 64MB cache buffer, and has a very intelligent multi-stream read ahead algorithm. So in practice, I think the performance is roughly equivalent.

The big difference is cost per GB. The Cheeta drives are much more expensive. I paid $600 for an 18GB Cheeta. The raw drive cost of a 180GB IBM/Hitachi is about $140. That's a 40 to one advantage. Even after I add my box, my electronics, and make some profit, I would guess there will be a 5 or 10 to one cost advantage to the end user. Also, five 180GB drives have the storage capacity of 50 18GB Cheeta drives, so the package is a lot smaller, requires a lot less power, and is much less likely to fail.

As for RAID3/5 functionality, I haven't focused much on the Quatrus with RAID3/5 yet. A question for Quattrus users:

Are you looking for redundant storage?

Best Regards,

Michael H. Anderson
Chief Engineer
Huge Systems

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