680W PS not enough to power 8 HD's?

[fotoobscura]

HI. I've had this odd issue where I can power 6 hard drives, even 7,
but cannot power 8. If I try to power the eighth one the drive won't
fully spin up. If I remove the 7th drive power connector and swap them
around (both) will spin up fine. So its definitely a power issue (the
drives have been tested fine).

What strikes me as odd is that a 680W power supply can't handle 8 HD's?

I've removed power to other devices (actually just the DVDr/cdr/etc)
but that didn't free anything up...and i'm a bit confused as to how to
solve this...

I do infact need all 8 HD's to work (and they must be internal because
they run off of a raid card) so i'm wondering if there are any thoughts
on how I could "free up" power elsewhere....(if that is indeed the
case)

This may be an irrelevant question but if i'm powering a ton of usb
devices (about 10- 3 off of mainboard, 7 or so off of a USB hub) could
that drain enough power from the PS?

THanks in advance for any advice.

 

[Paul Rubin]

What strikes me as odd is that a 680W power supply can't handle 8 HD's?

Could be the prob is the input current surge as all the drives try to
spin up simultaneously. At least with scsi drives, you could set it
up so the drives would spin up sequentially, slowing down booting a
little, but highly decreasing the peak load on the p/s. Maybe your
raid controller has a way to do that.

USB should use a maximum of about 2.5W per port.

 

[Michael Hawes]

HI. I've had this odd issue where I can power 6 hard drives, even 7,
but cannot power 8. If I try to power the eighth one the drive won't
fully spin up. If I remove the 7th drive power connector and swap them
around (both) will spin up fine. So its definitely a power issue (the
drives have been tested fine).

What strikes me as odd is that a 680W power supply can't handle 8 HD's?

I've removed power to other devices (actually just the DVDr/cdr/etc)
but that didn't free anything up...and i'm a bit confused as to how to
solve this...

I do infact need all 8 HD's to work (and they must be internal because
they run off of a raid card) so i'm wondering if there are any thoughts
on how I could "free up" power elsewhere....(if that is indeed the
case)

This may be an irrelevant question but if i'm powering a ton of usb
devices (about 10- 3 off of mainboard, 7 or so off of a USB hub) could
that drain enough power from the PS?

THanks in advance for any advice.

It may be the +5V rail that lacks the capacity. Does the raid card allow
a startup delay for the drives? They draw more power at startup than when
running.
Mike.

 

[Arno Wagner]

HI. I've had this odd issue where I can power 6 hard drives, even 7,
but cannot power 8. If I try to power the eighth one the drive won't
fully spin up. If I remove the 7th drive power connector and swap them
around (both) will spin up fine. So its definitely a power issue (the
drives have been tested fine).

What strikes me as odd is that a 680W power supply can't handle 8 HD's?

I've removed power to other devices (actually just the DVDr/cdr/etc)
but that didn't free anything up...and i'm a bit confused as to how to
solve this...

I do infact need all 8 HD's to work (and they must be internal because
they run off of a raid card) so i'm wondering if there are any thoughts
on how I could "free up" power elsewhere....(if that is indeed the
case)

This may be an irrelevant question but if i'm powering a ton of usb
devices (about 10- 3 off of mainboard, 7 or so off of a USB hub) could
that drain enough power from the PS?

THanks in advance for any advice.

My experience is that you should have about 30W per HDD for
(S)ATA drives with 7200rpm. Raptors and SCSI drives may need more.
This still overloads the PSU for some seconds, but a good one has
the reserves. After spin-up the real power consumption under
load dropps to something like a 15W maximum per drive.

I have one 12-disk system with dual Athlon MP 2800+ mainboard that
runns fine with a 550W Enermax PSU.

The USB devices get a maximum of 5V, 0.5A per port, i.e. 2.5W / port.

It is possible that your advertised as 680W PSU is a weakling.
Even if you have one of these insane graphics cards that take
in 200W, it should still be enough. More likely the marketing
department decided how much watts the PSU has and not the
engineers.

One other option is that you overload one 12V lane. Usually
you have 3 or 4 separate one for a PSU with this power
level. Maximum current may be as low as 15A per lane.
Now maximum perak current for spinup can be around 2.5A or
higher. With 8 disks this is 20A and may just be enough to
trigger overcurrent protection. If this is the case, then
you need to put the drives on different 12V lanes. On
the 550W enermax PSU, the thre lanes are recognizable by
cable color: One has pure yellow for 12V, the other has yellow
with a blue stripe and the thrid one has yellow with a black
stripe. Have a look into your PSUs manual to find out
how it is marked. Then just distribute the drives evely.

Arno

 

[Arno Wagner]

It may be the +5V rail that lacks the capacity. Does the raid card allow
a startup delay for the drives? They draw more power at startup than when
running.
Mike.

That is highly unlikely. 3.5" drives draw the majority of their
power form +12V.

Arno

 

[David Flory]

Could be the prob is the input current surge as all the drives try to
spin up simultaneously. At least with scsi drives, you could set it
up so the drives would spin up sequentially, slowing down booting a
little, but highly decreasing the peak load on the p/s. Maybe your
raid controller has a way to do that.

When I added my 15K SCSI drive to my moderately loaded system w/a Antec
Neo 550W power supply, the system wouldn't start up. Setting the drive
to wait for a start command solved the problem.

SATA supports staggered spinup. See if your RAID bios has a setting for
it. If they are SCSI drives, you can change a jumper on them to make
them wait for a start command from the controller (which will start them
one by one).

BR

Dave

 

[Rod Speed]

I've had this odd issue where I can power 6 hard drives, even 7,
but cannot power 8. If I try to power the eighth one the drive won't
fully spin up. If I remove the 7th drive power connector and swap
them around (both) will spin up fine. So its definitely a power issue
(the drives have been tested fine).

What strikes me as odd is that a 680W power supply can't handle 8 HD's?

Not really, the power supply capability is more complicated than it looks.

What matters for drive spinup is the current rating on the +12V rail
that powers the drive connectors. Modern high capacity power supplys
have at least one separate +12V rail thats designed to power the cpu
on the motherboard and that isnt available for spinning up the drives
and may not be anything special on the +12V rail that powers the drives.

I've removed power to other devices (actually just the DVDr/cdr/etc) but
that didn't free anything up...and i'm a bit confused as to how to solve this...

Some RAID cards can do a delayed spin up of some of the drives they support.

Or add another power supply to supply half the drives.

I do infact need all 8 HD's to work (and they must be internal because
they run off of a raid card) so i'm wondering if there are any thoughts
on how I could "free up" power elsewhere....(if that is indeed the case)

Its simpler to add another power supply or tell the raid card to delay the spinup.

This may be an irrelevant question but if i'm powering a ton of usb
devices (about 10- 3 off of mainboard, 7 or so off of a USB hub)
could that drain enough power from the PS?

Nope, thats on the +5V rail and the USB hub supply if thats a powered hub.

 

[Arno Wagner]

When I added my 15K SCSI drive to my moderately loaded system w/a Antec
Neo 550W power supply, the system wouldn't start up. Setting the drive
to wait for a start command solved the problem.

Not quite. The Antec PSU likely has a problem. Setting delayed startup
just evades the problem.

SATA supports staggered spinup. See if your RAID bios has a setting for
it. If they are SCSI drives, you can change a jumper on them to make
them wait for a start command from the controller (which will start them
one by one).

SCSI is far agead of SATA that way. IMO the jumper is the only
sensible solution. Simple and works. I have an old IBM 1GB SCSI
drive that had three different spin-up delays selectable by
two jumpers.

Arno

 

[mike]

HI. I've had this odd issue where I can power 6 hard drives, even 7,
but cannot power 8. If I try to power the eighth one the drive won't
fully spin up. If I remove the 7th drive power connector and swap them
around (both) will spin up fine. So its definitely a power issue (the
drives have been tested fine).

What strikes me as odd is that a 680W power supply can't handle 8 HD's?

I've removed power to other devices (actually just the DVDr/cdr/etc)
but that didn't free anything up...and i'm a bit confused as to how to
solve this...

I do infact need all 8 HD's to work (and they must be internal because
they run off of a raid card) so i'm wondering if there are any thoughts
on how I could "free up" power elsewhere....(if that is indeed the
case)

This may be an irrelevant question but if i'm powering a ton of usb
devices (about 10- 3 off of mainboard, 7 or so off of a USB hub) could
that drain enough power from the PS?

THanks in advance for any advice.

This is not a simple problem.
Power supply designs vary greatly, but here are some of the issues.

Each power output has a current rating. Multiply this rating by the
voltage to get the watts for that output. Sum up all these numbers and
you should get 680W. Problem is that reducing the load on one won't
guarantee you get more out of the others. In fact, you may get less,
see below.

Those power splits are designed for a typical system. Yours is far
from typical.

Hard disks take a lot more current to startup than run. Try staggering
the start. I'd also worry about data corruption. Drives draw a big
current spike when seeking. Eventually, you're gonna encounter a random
situation where they all seek at the same time. If this glitches
the power supply, you risk symptoms.

To save money, power supply designers try to minimize the number of
switching supplies operating off the line. ONE is optimum for cost.
There's often a dependency among the outputs. If your ratio of loads on
those dependent supplies is far from design center, you may not get
the regulation you expect. I've seen situations where INCREASING
the load on one supply increases the current capability of another.

For that same reason, if you add another big honkin' computer supply but
only
use the 12V for powering drives, you may find you can get a LOT less
than rated 12V current if you don't also load the other supplies.
Might be better to add a 12V-only regulated supply for the hard drives.
Pay attention to power supply sequencing issues.
mike

 

[David A. Flory]

Not quite. The Antec PSU likely has a problem. Setting delayed startup
just evades the problem.

I'm pretty confident in this PSU. I've run it 24/7 most of the time for
about 8 months now under varying loads. It stays cool running 7 hdd's
and a Radeon x1800, as long as spinup is somewhat staggered.

It's likely I had too many devices sharing one of the Antec's three 12V
rails.

My Fujitsu 15K needs 12V@3A on spinup, and combined with all the other
non-staggered ATA/IDE drives, and the graphics card, I'm not suprised
that one of the rails maxed out.

This PSU is supposed to be "smarter" than most, and I think it is
designed to shut down sooner rather than later if it detects a voltage sag.

Dave

 

[Folkert Rienstra]

Not quite. The Antec PSU likely has a problem. Setting delayed startup
just evades the problem.

So does PATA.

Doesn't help if the drive doesn't support it as well.

SCSI is far agead of SATA that way.

Stupid stupid babblebot, clueless as ever.
There have been such jumpers on some (S)ATA drives for years now.
You can even set it by software.
Take a nap babblebot, grow back a few braincells.

IMO the jumper is the only sensible solution. Simple and works.

I have an old IBM 1GB SCSI drive that had three different spin-up
delays selectable by two jumpers.

How ancient when you can have the controller start them instead.

 

[chrisv]

Stupid stupid babblebot, clueless as ever.
There have been such jumpers on some (S)ATA drives for years now.
You can even set it by software.

This is good information.

 

[Folkert Rienstra]

This is good information.

Unfortunately it doesn't do you much good if the bios (or your OS) doesn't
spin it up because it was never learned how to do that.
It's not the same as sleep mode. Just like SCSI it needs a specific command
to spin-up.