🚀 go-pugleaf

In article <22302@venera.isi.edu> rod@venera.isi.edu (Rodney Doyle Van Meter III) writes:
>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.
 I'd still like to know what his real application is:
    Can we make an effective index to reduce the number of 
    sides of disk?.

    We have 120 seconds worst case response required.  This is only
    time for about 4 mounts per drive (with current technology).
    It is stated that 5000GB of data has to be looked at randomly.
    Even if this only means the 10000 ( 5000GB/.5GB/side)
    are needed, we would require 2500 drives to get the maximum
    response time requested.   This would not include reading
    any significant amount of data on each platter.
 
 2500 *$3000/drive  + 15000*$300/slot = $7.5M + $4.5M = $12,000,000
 for 1GB optical disks for 15TB with 2500 drives.

 Hard disks are about $2000/GB, $2,000,000/TB, $30,000,000 for a
 15TB system.  If it turns out that you actually have to read through
 1/3 of the data in 120 seconds, then we have:
        5E12 bytes
       -----------      = 4E10 bytes/second
        1.2E2 seconds
 
  This would require about 4E10/4E6 fast disks, = 1E4 fast disks.
  Current technology is 2E9/disk, so 2E13 bytes would fit on
  this many disks, which is close to the 1.5E13 bytes needed in
  total, so the $30,000,000 should be still in the ballpark.
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