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Thread: Single vs. Multiple +12V rails: The splitting of the +12V rail

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    Default PSU for NAS application

    I read through the thread and have a question for the GURU(s) here...

    Suppose I'm building a PC-based NAS box that can support say 12 hard drives. This is done using a low power Atom based motherboard which has 6 SATA ports, plus an add-on PCI-E card that has 6 more SATA ports. No video card, no other peripherals other than some fans.

    Obviously the main power requirement here is for drive spin-up. Let's assume there is no staggered spin-up, so peak power requirements are say: 12 x 2.4A = 30A worst case on +12V? Some drives will draw far less than 2.5A on spin up.

    But in this situation, won't this choke a typical multi-rail PSU with overcurrent limited to effectively 19A or 20A?

    What PSU would be appropriate here? Does the single rail/split rail make a damn bit of difference here? How about the Seasonic S12II models (such as 380W version)?. Somewhere I read these are actually single-rail designs.

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    Ok.. I'll bite at your troll post.

    In your example, the spinning up of the drives WILL trip the OCP on most PSU's with split-up +12V rails because most PSU's put all of the SATA power connectors on one +12V rail. So to keep it simple you would probably want to use a PSU with a single +12V rail.

    Of course, to get to 12 SATA power connectors on most power supplies, or at least power supplies that are adequate for this job, you would have to use splitters and using splitters is working outside of the intended design of said power supply.

    On the other hand... a SilverStone 1500W, for example, has 12 SATA power connectors, but it's horrible overkill as you don't need anywhere near 1500W of power. A 500W will do. But a 500W will only have 4 to 6 SATA power connectors. But in the example of the ST-1500, the 12 SATA power connectors are split up across two +12V rails, each set to an OCP of 25A. So even though this PSU has multiple +12V rails (eight of them to be exact!), you would not trip the OCP on spin up.

    So the bottom line here is... simply do research and know what you're buying before you buy it. I think that goes without saying.

    I'm sure you realize that your example is an exception. Note that in my OP I said "99% of the folks out there single vs. multiple +12V rails is a NON ISSUE." That leaves 1% for the occasional weird config. I had used the example of "a plethora of Peltiers" in my post, but certainly you could make that "a plethora of hard drives."

    Anyhoo... Not sure why anyone would need that many drives for a NAS. With 1TB+ drive so cheap these days.. and you only need four drives to run a RAID5 with spare. Even if you wanted to use 5 or 6 drives for that, you have spanned data and double redundancy. Anything more than that is really overkill. Besides, if your motherboard has 6 SATA and you have a RAID card with 6 SATA (or even 8... I don't care), how are you going to span a RAID array across two different controllers (one on the mobo and one on the controller card)? I'd say just use five drives for RAID and one for OS. If you need capacity, take the money you'd save not buying a controller card and buy 2TB drives instead.

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    @Jonny; if you use Linux, you can actually combine two independent RAID configs via software.

    While it's also possible in Windows; there's a huge performance hit with it apposed to Linux's version.

    I'd say for the config of 12 HDD's a Cooler Master Silent Pro M 600w is most likely the best option.
    9 SATA Connectors
    5 Molex (obviously; use Adapters to turn them into SATA)

    Single 12v rail with 480w

    Gabe's review @ Hardware Secrets

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    Thank you for the reply, and honest, not trolling. Good to talk with someone who knows what they're talking about.

    Sure, I realize your site is mostly concerned with typical and high-end PC builds, but there are guys building NAS boxes as well.

    So yes, there are applications for large media servers. Typically, you can use, say 4-in-3 drive cages which require 2 molex connectors for power. So with three of these in a tower chassis, you require 6 molex connectors which is common.

    My question had more to do with labeling by PSU manufacturers. For example in your review of Seasonic S12 II Bronze 520W:
    http://www.jonnyguru.com/modules.php...Story&reid=185

    You say and the end of Page 1:
    This unit does not have two 12V rails at all - it's a single 12V design. There is no multirail overcurrent protection in there.
    Is this typical for the industry or for Seasonic in particular? Also, is this true for the other sizes of the Seasonic S12 II (eg., the 380W and 430W versions)?

    And I guess a related question, how would you really know how the rails are implemented short of taking the cover off and knowing what to look for?

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    Quote Originally Posted by tommt View Post
    My question had more to do with labeling by PSU manufacturers. For example in your review of Seasonic S12 II Bronze 520W:
    http://www.jonnyguru.com/modules.php...Story&reid=185

    You say and the end of Page 1:


    Is this typical for the industry or for Seasonic in particular? Also, is this true for the other sizes of the Seasonic S12 II (eg., the 380W and 430W versions)?
    Seasonic is usually the manufacturer that does it, but it is done by others as well. It's not typical, and it depends on the specific model.
    Quote Originally Posted by tommt View Post
    And I guess a related question, how would you really know how the rails are implemented short of taking the cover off and knowing what to look for?
    Unless the rail distribution is properly documented, there is no way to determine it other than taking apart the casing and examining the PCB.
    Main: i5 2500K@4.6GHz w/Zalman CNPS10X Performa, Intel DZ68BC, 8GB G.Skill DDR3-1600, PNY GTX 470 + EVGA GTX 470, ASUS Xonar DX, ADATA S510 120GB, Samsung 1TB F3+1TB F1+2TB F4, Kingwin LZG 1kW, Lian-Li PC-9F, Dell U2212HM+S2209W, Win7 Professional.
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    Zero82z has that one covered.... Seasonic is usually the one that says they have OCP then doesn't (their units, Corsair's and Antec's for example) and if the PSU company doesn't document rail distribution (or you don't see it in the review) then you can't really be sure.

    Tot: I figured that there must be a software solution that would let you bridge multiple controllers together, but yeah... GOD what a performance hit. I'd rather use fewer, larger drives on one controller than more drives on two controllers. So get the Zotac Atom board with the 6 SATA connectors, set five drives up for RAID-5 with spare and one drive for the OS and call it a day.

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    @Jonny

    Software solution in Linux actually isn't that bad. Bridging two PERC controllers (5/i & 6/i) only resulted in a 15% performance hit with minimal CPU usage using the Software solution in Linux.

    The 15% was calculated by doing some basic "expected" math.
    IE: Adding X drives to RAID B gains a XX% over X# of drives.

    If you've never checked it out; trying VM'ing FreeNAS
    It's a pretty beautiful tool

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    Thanks, but I'm happy with my simple 750i board's native RAID5+spare. I have four 500GB drives striped up which is plenty for my personal files.

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    Quote Originally Posted by jonnyGURU View Post
    Anyhoo... Not sure why anyone would need that many drives for a NAS.
    S'funny I was thinking just the opposite...but it all boils down to reliability and performance. You have to match the solution to the criticality of your data.

    We typically deploy 11 disks per RAID6 shelf, plus three online spares. Then we mirror the shelves so we don't take a performance hit if it needs to do a multi-disk rebuild. So that's 28 disks per volume...and we have 4-6 volumes per NAS.

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    Quote Originally Posted by jonnyGURU View Post
    Thanks, but I'm happy with my simple 750i board's native RAID5+spare. I have four 500GB drives striped up which is plenty for my personal files.
    Bah; not nearly enough.

    I've got 9 x 500 in my NZXT Whisper II Now that's some HDD love there. Not counting the 2 x 500, 3 x 250, +2TB drive in my Beta EVO.

    Granted the Whisper's only 80% full, and Beta has only 1.5TB of space taken up (roughly, could be a little more or a little less.)

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