Doug Siebert (foo@bar.bar) on 8/20/08 wrote:
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>>You're also talking about cheap MLC flash with an MTBF of less than 10,000 write
>>cycles. What's the availability on 2000 chips at 12h/day of full load? What's the
>>average read/write bandwidth? What's the cost to the host processor to deal with
>>2000 USB controllers? Can you even connect 2000 USB devices to a single system,
>>or are you stuck at 127 (not including hubs)?

The hardware reliability is a red herring: 2000 disks isn't reliable either, so you've got to have redundancy and fault-tolerance higher up in the system.

I don't see any particular reason why it's harder for the host cpu to handle a certain number of IO's per sec using USB rather than SCSI-like disk controllers.

And I'm pretty sure you can hang up to 127 devices off each USB controller, i.e. 4*127 off each PCI slot. So total number of devices isn't a showstopper.
>
>
>He's talking about systems designed to run the TPC benchmarks well, not work well
>in real world use for several years. The configurations being used in TPC benchmarks
>already bear little relationship to those used in the real world, so why not?
>
>Dunno about USB connection limits, but as the original poster points out, you can
>get four USB ports on a PCI card for $20, that lets you hook up 500 devices per PCI card.
>
>Anyway, I think the suggestion was somewhat tongue in cheek, poking fun at the
>silly designs used to run TPC benchmarks that are totally unlike anything anyone
>would design to run a real-world database (not just in storage configuration, its
>also true in terms of clustering used, DB layout, etc.)

It's not altogether serious :-) But I'm rather fascinated by the general strategy of exploiting cheap mass-produced technology to do more than it was designed for.
>
>I think the real problem would come in the per device write latency. Most of those
>cheap USB sticks allow fewer writes per second than even the slowest laptop hard
>drive, so thousands of such devices won't get you the IOPS of a couple thousand
>real disks. There are faster USB sticks out there, but then you are probably no longer at the $3/GB price point.

Ah. That makes sense. Thanks.