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SATA Only vs. SATA/SAS mixed

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October 7, 2011 12:52:57 AM

I have a Dell 690 Workstation. I have mulitple drives installed now, including a SAS pair in RAID 0 (270GB), a SATA SSD and a 1.8TB SATA Barracuda XT. In adding the last drive I noticed the arangement of the HDD connectors on the motherboard. 3 labeled SATA_0, SATA_1 and SATA_2, then 4 labeled HDD_0, HDD_1, HDD_2 and HDD_3.
When I read the manual on these the ones labeled SATA_x are definitely for SATA drives only. However the ones labeled HDD_x are either SATA or SAS.
My question is, are the SATA_x connectors optimized for SATA and therefore a faster channel, or will all 7 of these connectors be controled the same way (possibly even the same controller HW) and so any mix of SATA and SAS drives on the HDD_x connectors will work the same? Also, I believe the HDD_x connector bank may be the only place I can create a RAID setup for any SATA drives as I see no option to create a RAID under the BIOS for SATA only connectors.
Trying to optimize where I mix in the SATA drives and possibly another into a RAID. I have no choice but to leave the SAS drives where they are obviously.

More about : sata sata sas mixed

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October 7, 2011 4:51:32 AM
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Ok I have a Dell 690 standing behind me so I'll answer your questions.

The motherboard used in the 690 has two storage controllers. One is the Intel ICH9 (I think it's 9) which does the SATA / AHCI / IDE ports. Those are the three SATA 0~2 ports you see. It then has an on board SAS controller that does RAID and is for professional use. It's the HDD 0 ~ 3 ports.

SAS controllers are backwards compatible with SATA HDD's, but SATA controllers can't read SAS HDD's.

For your disks, put SAS disk in the SAS ports, and put SATA disks that you want enhanced performance on in the SAS ports. The SATA ports are for BD/DVD drives and any low performance SATA device you want to add. A SATA disk in a SAS port will function just like any other SATA disk but will get the benefit of the SAS controllers advanced performance and caching options.
October 7, 2011 10:33:06 AM

Excellent information. How about RAID? Am I correct that any RAID setup would need to be in the SAS ports? The SAS configuration program allows that. There is no mention of RAID in the SATA configuration.

(EDIT):
I read your reply again and I think the answer is in there. Sorry to repeat the question.
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October 7, 2011 12:30:41 PM

Best answer selected by bwhiten.
October 8, 2011 12:50:18 AM

Another question. I moved my SATA SSD over to the SAS ports and compared the benchmark numbers to what I had on the SATA only port. The numbers for sequential R/W were almost identical. However, the numbers for 4k and 4k-64 thread were worse by 50% or more. MY overall score dropped in half. I moved it back to retest and the performance went back to it's original number. Do I need to rebuild the drive from the SAS port, something else or would this be expected? Also as a test I removed all other drives from the SAS ports and ran the SSD alone. Low numbers again.
October 8, 2011 8:43:36 AM

bwhiten said:
Another question. I moved my SATA SSD over to the SAS ports and compared the benchmark numbers to what I had on the SATA only port. The numbers for sequential R/W were almost identical. However, the numbers for 4k and 4k-64 thread were worse by 50% or more. MY overall score dropped in half. I moved it back to retest and the performance went back to it's original number. Do I need to rebuild the drive from the SAS port, something else or would this be expected? Also as a test I removed all other drives from the SAS ports and ran the SSD alone. Low numbers again.


I haven't used a SSD disk on this controller before. You might want to check to see if there are any firmware / BIOS updates for the SAS controller. It sounds like the SAS controller is trying to "manager" your disk's I/O through buffering. The SSD might simply be too fast for the SAS controller to properly manage on it's own.

You might have to get the manual from Dell and try to see if there are some options you need to turn on / off on the SAS controller.
October 9, 2011 2:32:47 AM

Thanks. I'll look into it. Weird I did not get an email alert from Tom's after your post.
April 26, 2012 2:23:19 AM

I have 690 also, and i got a 60gb Mushkin deluxe SSD for it, and i first tried it in SAS port to only get 125mb/sec top read speed. I switched it to the SATA port and i got 255mb/sec top read speed, also windows index went from 7.2 in SAS to 7.8 in SATA port. I used HDTUne to bench the drive. I did same with the 150gb 10k Raptor i have in there, and it would only max out at about 120mb/sec on both SAS and SATA. So from my experience if u have an HDD it doesnt matter where u plug it in, if u have SSD then Definetly go with SATA port.
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