Can't build large SCSI array

[Jason]

foodog@uswest.net wrote:
>   You might check that your power supply(s) are beefy
> enough.  I've got some old DEC BA30? StorageWorks cabinets
> that'll do great with 6 RZ26 or RZ29 (1.2 or 2.? GB DEC
> drives) and the antique MYLEX controller it came with.
> Running the same cabinet off of an Adaptec AAA-131U2 adapter
> (SCSI-3) if you try to use 4GB and/or 10,000 RPM drives you
> can only use up to 4 drives.  No obvious problems when you
> plug in all 6, except that initializing the array _always_
> fails after about 10 minutes.  Adding a parallel power
> supply makes it go with all 6.

Sounds like the single power supply has about 95% of the power output
it actually needs to have (in amps) to run a 6 drive system, then, if
it takes THAT long to fail and works normally for spinup. 

Im surprised, actually - normally power supply problems with
multiple-drive systems are MOST obvious at spin-up - if nothing else,
the drives audiably take longer to spin up when the PS is overloaded.
But perhaps todays lighter faster drives actually use more power for
disk access?!?

I have a 4gb Sequel 5400 SCSI-2 lying around here somewhere.. its a
5200RPM 5.25 platter drive with 13 platters (26 heads, one for
tracking, gives 25 heads). When I got it in 1995 for only $10 used
(then RMA'd it since it was for a computer store BBS and under
warranty!) it was quite a deal! but if the room is over 70F the drive
overheats in a case.. it could tolerate 85F once I sanded off some of
the black plastic laminating the aluminum casing and attached a HUGE
heatsink fan (NOT a CPU one... about twice the size of an Athlon
heatsink heh)

Anyways, the point of all that, the above drive wouldnt always spin
up, even when it had its own power supply, after 4 years or so, until
I discovered that if I added several very large capacitors across the
12V line, it wouldnt overdraw the power supply for brief periods of
time, and actually complete the spinup process.

Since disk access and writing is such a transient thing, you MIGHT
have success with running your array of 6 drives on a single PS. If
nothing else, it IS worth looking into and testing because it might
open the possibility of being able to still run your system when one
of those power supplies dies someday, without the hassel of downtime.

-- 
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