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I know the throughput of a standard HDD doesn't quite saturate a 6Gb/s connection (if someone has a numerical value, that would be great). I have been told that the only way to reasonably saturate this is to put some SSDs in a RAID. How true is this?

EDIT When designing a configuration, what are good reference numbers (MB/s) to associate various HDDs and SSDs with (7200 rpm, 10000rpm; MLC, TLC, SLC)? When looking on a site such as NewEgg, there is no real speed listed, just the compatible SATA Ports (SATA III 6Gb/s)

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For your edit, if you want to know the write and read speed of hard drives, I think you need to look at benchmark tests. SSDs have such info directly in the specs, but HDDs don't. Probably, they don't have to and it's a pain to test (or painful for sales to reveal :p), so they don't test or show the results. Search for "<HDD1> vs <HDD2>" or "hard drive benchmark" or "<HDD> benchmark". I guess it's a bit like processors. They say what they want, but the end result isn't always exactly what you expect from the specs. RPM are vaguely an indication of physically possible speed, but zero reliable. –  Ariane Jan 11 '13 at 18:08
    
Good point. I had intended on vaguely designing my new setup with estimated numbers, then looking up benchmarks to fine tune my design. It wouldn't be a bad idea to start with researching benchmarks. –  Jeff Jan 11 '13 at 18:43
    
Mhm. I haven't looked for HDD benchmarks, but for CPU ones, you have graphs of which are best, with the price as well, and price/quality rate graphs too. So you can basically do your shopping there. Unless you find a super interesting special deal. :p –  Ariane Jan 11 '13 at 18:53
    
@Ariane RPM should be multiplied with density per platter, as well factor in the number of platters. –  Hennes Jan 12 '13 at 0:06
    
@Hennes: R-right. *Feeling very unknowledgeable* –  Ariane Jan 12 '13 at 1:43

1 Answer 1

up vote 3 down vote accepted

How true is this?

Partially. A SATA-III 6.0gbit per second connection has a maximum throughput around 550MB/sec.

Anything on a SATA-III bus which can deliver those settings on a single channel will max that out. Right now there are only two common setups which reach those speeds:

  1. A fast SSD (RAID does not factor in this, since it is per channel, and you would put each SSD on its own SATA channel).
  2. Port multipliers (which fan out to multiple SATA devices. Either SSD, HDD, or a combination).


Edit, answering the OP edit:

Current convential HDD speeds are:

  • 2½ inch laptop drives: about 60-90mb/SEC
  • Desktop drives: around 100MB/sec
  • 15k RPM high end enterprise SAS drives: Up to 200MB/sec on the outer tracks

Curent SSD speeds can max out a SATA-III channel on higher queue dept sequential reads.

For current day SSD speeds, check benchmark sitrs or generic hardware sites. (e.g. Toms Hardware, though that one is slowly moving from an informative site to a clearly sponsored site).

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Additionally, I find it funny how we have fast cables (and I'm not even sure SATA III is the fastest we have), so fast that most devices can't use its full power. Cool in a way, to know things can evolve without too many bottleheads downstream. –  Ariane Jan 11 '13 at 17:21
    
Fast designs then current generation devices need just means it will last a few years before we have to change/upgrade. –  Hennes Jan 11 '13 at 17:22
    
In response to 1. Would you not be able to put two SSDs in a RAID 0 configuration to obtain faster speeds on the same channel? –  Jeff Jan 11 '13 at 17:34
    
@Jeff I believe the RAID controller puts the bar higher, as well. So yeah, more data is going through, but more data is able to go through as well, so still no saturation. I've never seen RAID with my own eyes, but I figure it's not plainly two drives plugged into one motherboard SATA output through a controller, yes? That would be a dumb splitter. –  Ariane Jan 11 '13 at 17:39
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A hardware RAID card communicates via the motherboard though a PCI or PCIe slot. Thus it does not use te motherboards SATA ports at all. Depending on the card it will either supply its own SATA or SAS ports. Each of those is often connected to a drive or to a port multiplier. –  Hennes Jan 11 '13 at 18:57

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