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I am thinking of building a cheap home server and found a server chassis which holds 12 SATA drives.

I'm looking at this motherboard, but I am having a hard time understanding how to fit 12 drives onto it.

It has 6 onboard SATA ports for storage, which means I have to buy some sort of expansion card to fit the other 6. The PCI-e interfaces supported by this motherboard are two x8 and one x4.

I decided I want to use RAID 10 on the array.

Three questions:

  • If I'm using the 6 onboard SATA ports, does it make sense to buy RAID cards to support the other 6 drives? Is it either using RAID cards for all 12 of the SATA drives or none?

  • Will PCI-e 2.0 work with either PCI-e x8 and PCI-e x4? I'm looking at this raid card which seems cheap. I could buy 3 and that would solve the problem. (the same question applies to SATA expansion cards)

  • Does it matter if the PCI-e SATA expansion cards use SATA 6 Gb/s while the onboard uses SATA 3 Gb/s in a raid 10 setting?

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2 Answers

up vote 2 down vote accepted

Ypou asked three questions. Lets start with this one:

Will PCI-e 2.0 work with either pci-e x8 and pci-e x4?

Yes, it will work. But you are mixing up two different things:

PCI express comes in several versions.
PCI-e version 1 supports up to 2.5 Gbit/sec per lane.
PCI-e version 2 supports up to 5.0 Gbit/sec per lane.
PCI-e version 3 supports up to 8 Gbit/sec per lane.

Each of those can use single lanes, or combine several of them. That is what the x8 and x4 stand for.


Does it matter if the PCI-e SATA expansion cards use SATA 6 Gb/s while the onboard uses SATA 3 Gb/s in a raid 10 setting?

No. Both 3.0 Gbit/sec and 6.0 Gbit/sec SATA connections are a lot faster then any rotating disk. (Best speed on spinning HDDs is about 200 MB/sec, while SATA II / SATA 3.0 allows for transfers up to 270 MB/sec. The only reason to buy anything with a higher speed is if you use a SSD, if you want to future proof your purchase, or is the faster version is cheaper.


If I am using the 6 onboard SATA ports, does it make sense to buy RAID cards to support the other 6 drives? Is it either using raid cards for all 12 of the SATA drives or none?

That depends on how you want to use it. If you use software RAID then it does not matter how you access the extra drives. If you want a hardware RAID card to manage several drives than all those drives need to be connected to that hardware RAID card.

For these, first consider how you want to use the drives. Read this post on our sister site SF and make a choice.

Then decide on software or hardware RAID. Software RAID tend to work well for most situations, but HW RAID might be a better choice when doing RAID 6 or RAID 60.

Only then decide if you want to buy a (16, or 12+ port) HW RAID card, or if you want another solution. Other solutions include plain host adaptors ('aka SATA/SAS cards'), or port multipliers.


(Since you were considering RAID 10, software RAID might be the cheapest solution.)

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PCIe 3.0 supports 8000 Mbit/sec per lane (7880 taking encoding into account). –  Dennis Mar 19 '13 at 21:22
    
My major concern was the unit. I think you meant Gbit, not mbit. –  Dennis Mar 19 '13 at 21:28
    
What are lanes? –  That Brazilian Guy Mar 20 '13 at 1:46
1  
A lane is a point to point connection between two PCI-e devices. Think of it as a wire. I can either serialise the information (chop it into pieces of 1 bit and then send those one by one), or I can use a few in parallel. PCI-e has chosen to use the one by one approach. Even you use multiple lanes you get multiple 1:1 connections. E.g. PCI-e x4 uses 4 'wires', not one cable with signal width 4. –  Hennes Mar 20 '13 at 12:49
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The answer depends upon whether you want to use hardware or software RAID. Software RAID (OS-dependent) should be capable of spanning any connected drives regardless of which card/connector/speed is used. Hardware RAID, managed by the HBA, is a lower-level solution, but can only manage the drives attached to that particular card/piece of hardware. Also, that card (or any x1 PCIe) will work in any of your PCIe slots. You'd likely want to use your lowest speed slot (x4 appears to be your lowest speed PCIe slot according to the info you provided), as it's not going to take advantage of anything more than that for which it's specified.

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