DIY NAS build - SATA 3Gbps vs 6Gbps

I'm putting a DIY NAS build together to replace my Synology DS214 Play. I'm using my old i7-3770 and some RAM I have left over since my old motherboard in my main PC died and I've got hold of a MSI H61I-E35 motherboard. I'll be reusing the WD 3TB Caviar Red drives from the Synology for now.

The MSI board has 4x SATA ports but they're "only" 3Gbps and the drives have 6Gbps interfaces. I know this will work but is that likely to significantly reduce performance, i.e. are these drives capable of reading/writing at more than about 3Gbps?

If so then the board does have a PCIe x1 2.0 slot so I guess I could get a little SATA controller card and use that for the NAS disks and keep the OS device on a USB stick or small SSD. 1 lane of PCIe v2.0 is quoted as "5 GT/s" on wikipedia, does that equate to 5Gbps? If so then I guess that'll still be a limit on the full 6Gbps the drives are theoretically capable of but probably not so much that it'd have a real impact?

I would say that unless you're using 10GB/s networking, you're almost certainly going to be bound by the network and the speed of the spinning rust. Just plug them in to the 3Gbps ports.

3 v 6Gbp SATA only comes into play with SSDs.

AFAIK there's not a spinning rust disk in the world that can saturate a 3Gbps SATA interface. 6Gbps interfaces on HDDs are for marketing purposes rather than performance. Use your 3Gbps ports. You'll lose nothing.

Thanks folks, I thought as much but thought I'd check anyway.

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Originally Posted by 8bit

1 lane of PCIe v2.0 is quoted as "5 GT/s" on wikipedia, does that equate to 5Gbps? If so then I guess that'll still be a limit on the full 6Gbps the drives are theoretically capable of but probably not so much that it'd have a real impact?

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It does but that's without overhead. Throw in the 8b/10b encoding and you're down to 4Gbps and your actual data rate is below that.

SATA figures are signalling rates too though, so PCI-E 2.0 1x is probably around 80% of the speed of SATA 6Gbps in practice. Although obviously all drives on the controller share the link instead of having one each.

A hard drive can exceed SATA II (3Gbps) speeds for cached data but not for any sustained transfers.

Your limiting factor will likely either be your ethernet connection (if it's Fast Ethernet) or your the drives themselves. The links inside the computer will rarely be a limitation.

Thanks for the clarification. The network in question is 1Gbps wired so yeah, clearly a simple file transfer over CIFS or NFS is going to be limited to that. The server will also run Plex Media Server however and will be transcoding video (mostly HD) on the fly, hence why I was thinking about performance of the underlying storage subsystem.

If it is possible use two Gbit Ethernet ports on your motherboard then you have 2Gbps, but again unless you are using SSDs in your RAID there is no way you will fully saturate SATA3 on the remote host

My (unraid therefore no speed increasing RAID) NAS has ALL of its HDD running on SATA 3Gbps and also Emby which does transcoding. I never experience any issues at all. Transcoding is usually not as dependant on the HDD transfer speeds as it is processing power.

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Originally Posted by username2

If it is possible use two Gbit Ethernet ports on your motherboard then you have 2Gbps, but again unless you are using SSDs in your RAID there is no way you will fully saturate SATA3 on the remote host

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Using 2x 1Gbps doesn't simply give you 2Gbps even if you team or bond the interfaces; any one destination host will only ever use one of the network interfaces to talk on (how they're selected depends on several things) so the best you'd hope for would be two separate clients each getting fully 1Gbps full duplex to and from the machine.

In any case, the board in question only has a single 1Gbps NIC so that's not really an option, not without adding a PCIe NIC and I want to use the single PCIe slot for a USB 3.0 interface.

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Originally Posted by 8bit

Using 2x 1Gbps doesn't simply give you 2Gbps even if you team or bond the interfaces;

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No obviously it wouldn't in the real world even 1Gbit connection is not likely to hit 1Gbit transfer. I was just trying to prove a point that satas 2 or 3 won't matter.

Sure, for simple file transfers over NFS, CIFS etc. then yes, 1Gbps is going to be the limit. As above, I was thinking more for internal stuff like video transcoding etc.