🚀 go-pugleaf

In article <1992Aug31.043738.19685@psg.com> randy@psg.com (Randy Bush) writes:
>vhs@rhein-main.de (Volker Herminghaus-Shirai) writes:
>
>> I need to design a retrieval system for ~15TB of data, of which ~5TB are
>> retrieved with a high frequency (25 requests/second) and an access time
>> of avg. 30 seconds (max. 120 seconds). Retrieval lacks any locality, so the
>> 5TB are real random-access. The rest of the data is still accessed at a
>> rate of 5 requests/second.
>
>Optical RW store, a la HP.
>-- 
>randy@psg.com   ...!uunet!m2xenix!randy


The problem is not the volume -- 15 TB is huge but not enormous
(like the distinction?:-)), the problem is the access rate. Even
the fastest cart machines are ~15 seconds to replace a disk or tape
(remove the AND insert the new), so to get 25 reqs/sec., you're
looking at not 40 but 400 cart machines.

As pointed out, you probably want MO, not tape; VHS, 8mm, D-1, and
D-2 are all fairly slow to load (I think Ampex' D-2 is the fastest),
plus the seek times... w/ 400 cart machines, you'll have enough
drives that seek time isn't a problem with your latency.

An important question is the size of an average data request --
if it's a bank account balance, the throughput of the device is irrelevant.
If it's CAD files or fluid-flow simulation, you need one of the
higher-speed alternatives.

Are you prepared to handle acres of floor space, hundreds of
drives, all the power, etc.?

By the time you add it all up, I think the only realistic solution
is RAID arrays. Yes, they're small and expensive, but I think it's
the only way to get that kind of throughput.  Oh, you'll need
one mini-super for every several RAID arrays, too, don't forget.

What's the timeframe for implementation?  The capacity is
easy, if not quite off-the-shelf, but meeting those performace
characteristics is damn near impossible in the current generation
of devices.

		--Rod

disclaimer: I work for a company with a vested interest in this
area, but you don't know which one, so there! It's not the only
company mentioned by name in this article.