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Discussion Starter #1
Earlier today someone posed me a question - do drives perform slower if you're accessing a whole bunch at the same time?

Well, the answer is "Yes", right? Unless you've got a super fast Intel SATA controller, it's logical that if you max out 4+ drives on the same one, that controller is going to be struggling to keep up. But just how much of a hit would it be? 1%? 2%? 5%? 20%?

So I started running HDTune benchmarks on my lone drives. I started with solo benchmarks, then duo, then trio, then all four at once...

To my surprise, SB850 showed no slowdown whatsoever. I don't know if it's the best controller for SSDs, but it seems like it would cope just fine with large HDD RAID arrays.

Now for the proof and benchmarks.

Process Explorer:
hdtuneproahcibenchmarkp.png


At 460MB/sec+, access times and sequential speeds are not affected in a negative way...

HDTune:

First row is solo benchmarks. Second row is obviously all four running at once. I skipped including the duo/trio benchmarks, as they merely show the exact same thing as the test on four at once.

hdtuneproahcibenchmarkc.png


It almost seems like the SATA controller performs better when being hit by multiple requests... but it's more likely that there's a slight margin for error.

If I had more drives, I'd be testing with a fifth and sixth to find out what MB/sec SB850 finally caps at. I suspect it's somewhere between 460-600MB/sec, but I could be proven wrong for all I know.
 

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Discussion Starter #3
I also ran Random Access tests, with no noticeable impact from benchmarking multiple drives. (Again, some benchmarks went up slightly, some went down slightly)

And I tried mixing them. (the Benchmark tests and Random Access tests) Again, no difference. Near as I can tell, latency and throughput are not affected at all by as few as four current-generation HDDs.
 

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The ALink Express III that connects the SB850 to the rest of the chipset has 2GB/s of bandwidth. I wouldn't expect major limitations in drive performance with only four drives connected.
 
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Discussion Starter #5
Quote:
Originally Posted by Blameless;14566372
The ALink Express III that connects the SB850 to the rest of the chipset has 2GB/s of bandwidth. I wouldn't expect major limitations in drive performance with only four drives connected.
But what's the SATA controller capable of?
wink.gif


Good to know that there's plenty of bandwidth available. One of the many complaints about boards with Marvell SATA3 controllers is they usually have two ports connecting through a single 500MB/sec PCIe lane. That's not good - especially for SSDs.
 

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Discussion Starter #6
Well, to conclude the thread - no slowdown with 6 drives.

I'm not sure where it'd start to show. I'd need a bunch of SSDs to find out.





Quote:


Originally Posted by Blameless
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The ALink Express III that connects the SB850 to the rest of the chipset has 2GB/s of bandwidth. I wouldn't expect major limitations in drive performance with only four drives connected.

I read up on it a bit.

http://en.wikipedia.org/wiki/Compari...nk_Express_III

Do you think SB850 can come close to providing 2GB/sec bandwidth? Most affordable PCIe RAID controllers can't, so I'd expect it to cap far lower.
 

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Discussion Starter #8
What are you running your benchmarks in? What software? What stripe size did you set up for your RAID?

SSDs are not HDDs - I've heard that smaller stripe sizes are actually better for them.

If you're benching in HDTune, play around with the block sizes and see what happens.

It's also possible that your SSDs just don't like RAID. (Sandforce controllers appear to be quite ornery.)
 

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Thanks.
Independently of how true everything you said is, note:
same drive, same OS, same install, same everything, same SATA port
With AHCI mode in BIOS, win7 uses AMD Sata or MS AHCI driver, and I get 500MB/s
With RAID mode in BIOS, win7 uses AMD AHCI Compatible RAID driver, and I get 320MB/s. Also note, despite RAID mode, it's a standalone drive, not part of any raid, so presumably the AHCI aspect of the raid driver is used.
So, why not same speed?
Thanks anyway
SM
 
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