Mixing SAS and SATA drives - working (with correct hyperlinks)

Jeremy Cole jeremy at provenscaling.com
Tue Mar 4 17:28:57 CST 2008


Hi Radim,

That card you're looking at is called an "interposer" and makes the SATA 
drive pretend to be a SAS drive in order to allow it to support more 
advanced features that SAS supports, and to run in SAS environments. 
The interposer card provides the following features:

* Dual Port -- SAS drives have the ability to be connected in an 
active-active manner to two controllers simultaneously.  This is what 
the extra pins on the interposer card are for.

* Boost Signal Voltage -- SATA drives run at a lower signal voltage than 
SAS, so the interposer card boosts the signal voltage to SAS levels.

* Command Set -- The interposer card understands the full SAS command 
set and drives the SATA drive using the more limited SATA command set.

* WWN -- SATA drives are identified on the bus by the port they are 
connected to.  SAS drives are uniquely identified by a WWN (World Wide 
Name) which doesn't change when they are moved from slot to slot.

There are a few caveats with the SAS vs. SATA and mixing them:

* If you want to run SATA drives in an external enclosure such as the 
MD1000, you should normally have interposer cards on the drives.

* If you mix SATA (without interposer) with SAS on the same controller, 
all drives will run at the lower SATA signal voltage instead of the SAS 
voltage, and you may experience strange behaviour.

It might not be a bad idea to read up here:

http://en.wikipedia.org/wiki/Serial_Attached_SCSI#SAS_vs_SATA

Regards,

Jeremy

Radim Hejc wrote:
> Sorry, there was wrong hyperlinks for all pictures, all pointing to one 
> wrong picture, so here is correct letter again :)
> 
> -----------------------
> 
> After some experiments i found following
> original caddies with sata drives from Dell looks like this
> http://www.mixx.org/dell/sata_red.jpg
> 
> IMHO that whole reduction is there to add these pins
> http://www.mixx.org/dell/sata_pins.jpg
> these pins are always on SAS drives connectors, but these are regular on 
> SATA connectors, dell reduction add them also for SATA drives,
> does enyone know what  are these for? is just for hotswap?
> 
> (i found some info on SUN 
> http://docs.sun.com/source/820-0046-10/appc-pinouts.html it seems that 
> these pins
> have just Ground and no signal)
> 
> 
> Weird thing is - when you connect to backplane SAS drives togehter with 
> original caddies from dell (SATAu)with reduction
> PERC6/i has problems as i described before
> 
> As i have spare caddies without reduction  (SATA) which i bought on Ebay 
> for $15 for piece i conenct two Seagate 750GB spare drives
> to them and found this interresting thing
> 
> When you connect caddies with SAS together with caddies with SATA drive 
> without this Dell reductions
> as here http://www.mixx.org/dell/sata_no_red.jpg everything works 
> without any problem :)
> 
> Does anyone has an explanation?
> 
> Drives was connected as twice RAID1 - one for SAS and one for SATA 
> drives, tried on PE 2950 with PERC6/i controller
> 
> 
> R.H.
> 
> Radim Hejč
> IT infrastructure
> U-TURN, a.s.
> Argentinská 38/286
> 17000 Praha 7, Czech rep.
> 
> 
> 
> 
> Tony Molloy wrote:
>> On Tuesday 04 March 2008 16:35:33 Radim Hejc wrote:
>>   
>>> I was trying today to mix two 76GB SAS 15krpm Fujitsu drives and two
>>> 750GB Seagate SATA drives together
>>> (2x RAID1 both Dell Originals) on PE 2950, but after server reboot i'm
>>> still getting messages about Foreign configuration
>>> from PERC/6i controller, then one of SATA drives is always degraded.
>>> When i removed SAS everything seems to work fine
>>>
>>> strange thing, i will research more
>>>
>>>     
>>
>> That's interesting. That suggests that you can't mix them on the same 
>> controller even if they are separate RAID arrays. I'll be interested to hear 
>> what you come up with.
>>
>> In the end I could always go with all SATA drives. It would be cheaper ;-)
>>
>> Tony
>>
>>   
>>> Radim Hejc(
>>> IT infrastructure
>>> U-TURN, a.s.
>>> Argentinská 38/286
>>> 17000 Praha 7, Czech rep.
>>>
>>> Tel.: +420.777190160
>>> ICQ: 11064792
>>>
>>> Tony Molloy napsal(a):
>>>     
>>>> On Tuesday 04 March 2008 11:11:56 Mark Watts wrote:
>>>>       
>>>>> On Tuesday 04 March 2008 10:51:12 Tony Molloy wrote:
>>>>>         
>>>>>> On Tuesday 04 March 2008 09:49:37 Hostmaster wrote:
>>>>>>           
>>>>>>>>>> Can't mix SATA and SAS disks. So we can't supply 2X73GB, SAS,
>>>>>>>>>> 3.5-inch, 15.000 rpm Hard Drive 4X750GB, SATA, 3.5-inch, 7200 rpm
>>>>>>>>>> Hard Drive. Instead I've configured 2X73GB, SAS, 3.5-inch, 15.000
>>>>>>>>>> rpm Hard Drive 4X400GB, SAS, 3.5-inch, 10,000 rpm Hard Drive.
>>>>>>>>>>                   
>>>>>>>> Can I do this and if I can how do I get Dell to supply me with that
>>>>>>>> configuration.
>>>>>>>>               
>>>>>>> AFAIK its *technically* possible to mix them, however it isn't a Dell
>>>>>>> supported configuration, therefore they won't sell them that way.
>>>>>>> Several of the guys from Enterprise Storage frequent these lists, so
>>>>>>> they will be able to give you the final word, but it might just be
>>>>>>> easier to buy the server with the supported config (ie just the two
>>>>>>> SAS drives for the OS), and then put a separate order for the four
>>>>>>> SATA drives, but check with someone who knows the PERC6/i better than
>>>>>>> me before buying!
>>>>>>>             
>>>>> This question has been asked before.
>>>>>         
>>>> As I said in my mail I know it has been asked before but I'm just about
>>>> to spend 50,000+ euros on a rack so I wanted to be sure.
>>>>
>>>>       
>>>>> You can mix SATA/SAS disks on the same backplane, but the cannot be in
>>>>> the same logical volume.
>>>>>         
>>>> That was my impression of the previous thread so my RAID1/RAID5
>>>> configuration should work. The problem then is to get Dell to sell that
>>>> configuration to me.
>>>>
>>>> Thanks,
>>>>
>>>> Tony
>>>>
>>>>       
>>>>> http://lists.us.dell.com/pipermail/linux-poweredge/2008-February/035159.
>>>>> htm l
>>>>>         
>>>> _______________________________________________
>>>> Linux-PowerEdge mailing list
>>>> Linux-PowerEdge at dell.com
>>>> http://lists.us.dell.com/mailman/listinfo/linux-poweredge
>>>> Please read the FAQ at http://lists.us.dell.com/faq
>>>>       
>>
>>
>>
>> _______________________________________________
>> Linux-PowerEdge mailing list
>> Linux-PowerEdge at dell.com
>> http://lists.us.dell.com/mailman/listinfo/linux-poweredge
>> Please read the FAQ at http://lists.us.dell.com/faq
>>   
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Linux-PowerEdge mailing list
> Linux-PowerEdge at dell.com
> http://lists.us.dell.com/mailman/listinfo/linux-poweredge
> Please read the FAQ at http://lists.us.dell.com/faq

-- 
high performance mysql consulting
www.provenscaling.com



More information about the Linux-PowerEdge mailing list