lkml.org 
[lkml]   [2003]   [Apr]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [ANNOUNCE] udev 0.1 release
On Fri, 11 Apr 2003, Mike Dresser wrote:

> On Fri, 11 Apr 2003, John Bradford wrote:
>
> > [Puzzle]
> >
> > Say the power supply had five 5.25" drive power connecters, how many 1
> > into 3 power cable splitters would you need to connect all 4000 disks?
>
> never seen a 3 into 1, but we'll play along.
>
> every 3 in 1 connector you use, triples your connections, go two
> levels deep, it's 3 * 3 = 9, pretty obvious.
>
> I'm just going to use one connector off the power supply for now.
>
> 3 ^ 7 = 2187
>
> So we'll use another two off the PS and not go as deep
>
> 2 * (3 ^ 6) = 1458
>
> 2187 + 1458 = 3645
>
> Need another 4000 - 3645 = 355
>
> 3 ^ 5 = 243.
>
> Need another 355 - 243 = 112
>
> Use another connector
>
> 3 ^ 4 = 81
>
> Need another 112 - 81 = 31. So close but out of first level connectors.
>
> So I put a 3 way splitter on one of those.
>
> 3 ^ 3 = 27. argh!
>
> Need another 31+1(had to use up a connector) - 27 = 5.
> So I put another 3 way splitter. 5 + 1 = 6.
>
> 3 ^ 1 = 3. Need another three. Take one off, pass it around, and we're
> almost done. Add another 3 way splitter, we've got two connectors left
> over, and everything is plugged in. Turn on the ps. Boom, done.
>
> Now, to count up the total.
>
> level 1 = 1 = 1
> level 2 = 1 + 3 = 4
> Level 3 = 4 + 9 = 13
> Level 4 = 13 + 27 = 40
> Level 5 = 40 + 81 = 121
> Level 6 = 121 + 243 = 324
> Level 7 = 324 + 729 = 1053
>
> So anyways, I used one level 7, two level 6's, one level 5, one level 4,
> one level 1, one level 3, one level 1, another level 1 and finally another
> level 1
>
> total of 1053 + 324 + 324 + 121 + 40 + 1 + 13 + 1 + 1 + 1
>
> I come up with 1879.
>
> If i'm too high, that's to account for the fact you broke some connectors
> at some point, so you used the spares.
>
> If i'm too low, that's to account for the fact that out of 4000 drives, a
> few are going to be DOA and you couldn't hook them up anyways.
>
> Someone PLEASE tell me the simpler way to do this.
>
> Mike
>



Every three-connection connector supplies power to two drives.

|--------D1
-----|--------D2 ________D3
|______________|_______D4
|_______Continue
If you have 4000, drives, you need 2,000 connectors if you only
had one power cable to start. Or 'N' power cables! The number
of power cables doesn't count! Note that you can only
add drives in "2s" so odd-numbers of drives give you an extra
connection. Also, for the limit-check, you need 0 connectors
if you have 4000 lines to start, and 1 connector on each line
if you have 2000 lines, (look above, 2,000 connectors). Now,
if you have 1000 lines, you need 2 connectors for each line.
That's still 2000 connectors!
If you have 500 lines, you need 4 connectors for each line.
That's still 2000 connectors!
If you have 250 lines, you need 8 connectors for each line.
That's still 2000 connectors!
.etc!


Cheers,
Dick Johnson
Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:34    [from the cache]
©2003-2011 Jasper Spaans