SAS vs. SATA backplane

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sphinx99

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Looking at a chassis for a storage server, something on the order of 20 disks. I'm hoping to clarify my understanding of some things, especially in the area of the backplane. Specifically, I'm hoping someone can review the below and let me know if my thinking is off anywhere.

I understand that an internal backplane (to support hot-swap etc.) can have different connectors to support SAS disks (data and power), SATA, or in the case of something like SFF 8482, the backplane can support either sort of disk. The backplane itself is not intelligent; it still needs to be plugged into a RAID controller that supports SAS or SATA. There are controllers for SAS, for SATA or for both. For every drive connected to the backplane, there will be a cable from the "inside surface" of the backplane to the controller, and possibly another to the power supply for power. So the backplane merely permits hot-swap without having to crack open the case--convenience feature.

Therefore if I wanted to keep my options open over a five year horizon and still shoot for hot swappability, I should look at a chassis with a backplane that supports both types of drives (e.g. SFF 8482 connectors) connected to a controller that supports SAS and SATA. Then in theory I may be able to mix and match. However, I should not expect to create a physical RAID volume that spans a heterogenous mix of SAS and SATA disks; if I do mix up my disk types, I might end up having RAID volumes based off the SAS spindles and other RAID volumes based off the SATA spindles.

Also, if I'm looking at the popular and inexpensive Norco 4020 case, that's SATA only so no point in SAS. If I want a case with comparable number of drive bays that uses SATA-compatible SAS connectors on the backplane, I'm going to spend far more money for it. (But how much more? Any suggestions?)

Lastly, if I want to eschew a hot-swap backplane altogether, then my choices open up greatly: I simply buy a server case with enough internal drive bays (one of the Lian Li monsters perhaps) and I can mix and match spindle types to my heart's content, as long as I have appropriate controllers off the bus to provide ports. The cabling will be messier and I may not have hot swap (or is hot swap possible with some sort of tray??) but the chassis itself won't limit me to any particular data transfer protocol.

Does this all make sense?
 
You don't need to use multilane cables for a SAS backplane (or period for that matter). The Norco 4020 will do both SATA and SAS...
 
Trust us, that 4020 Norco is awesome. A single 5in3 (or 4 in 3 for that matter) hotswap dock for SATA/SAS (SAS is backwards compatible with SATA cabling) can run you about a hundred dollars. That case provides true scalability. You could attach 10 SATA drives, then 10 SAS (no need for new hardware, those docks will take them) drives when your budget allows.

Would get one of those cases myself, were it not for this crappy economy and lack of a job. I've maxed the ports out on both my controller cards, and case.
 
You do get what you pay for though, and the quality is not on par with the Supermicro cases. Then again, those cost 3x the price, so what can you expect? I don't trust my data and drive arrays to a Norco case, but if it is strictly for Media server builds and etc. then a Norco might be ok.
 
My only corcern with the Norco would be if you swap drives on a regular basis. Sometimes the trays on the Norco are a little stiff. Still though, I would trust the Norco case to do anything a Supermicro would. I wouldn't have any hesitation in putting anything at my house in a Norco, whether it be arrays or data or whatever.
 
sphinx99 said:
I understand that an internal backplane (to support hot-swap etc.) can have different connectors to support SAS disks (data and power), SATA, or in the case of something like SFF 8482, the backplane can support either sort of disk.
Click to expand...

A SAS backplane is backwards compatible with SATA drives.

The backplane itself is not intelligent; it still needs to be plugged into a RAID controller that supports SAS or SATA.
Click to expand...

Correct, backplanes don't do a whole lot on the logic side until you move into the realm of SAS expander backplanes.

For every drive connected to the backplane, there will be a cable from the "inside surface" of the backplane to the controller, and possibly another to the power supply for power. So the backplane merely permits hot-swap without having to crack open the case--convenience feature.
Click to expand...

Typically, yes.

Therefore if I wanted to keep my options open over a five year horizon and still shoot for hot swappability, I should look at a chassis with a backplane that supports both types of drives (e.g. SFF 8482 connectors) connected to a controller that supports SAS and SATA.
Click to expand...

Most backplanes in new cases are now SAS. Supermicro switched to all SAS backplanes in their new cases.

Then in theory I may be able to mix and match. However, I should not expect to create a physical RAID volume that spans a heterogenous mix of SAS and SATA disks; if I do mix up my disk types, I might end up having RAID volumes based off the SAS spindles and other RAID volumes based off the SATA spindles.
Click to expand...

If you wanted to...

Also, if I'm looking at the popular and inexpensive Norco 4020 case, that's SATA only so no point in SAS.
Click to expand...

The manufacturer specs say the chassis uses SAS backplanes.

If I want a case with comparable number of drive bays that uses SATA-compatible SAS connectors on the backplane, I'm going to spend far more money for it. (But how much more? Any suggestions?)
Click to expand...

I'm all about Supermicro (it's what we sell at work), but a 16 bay Supermicro case will run you $800-900+ due to the redundant server PSU.

Blue Fox said:
You don't need to use multilane cables for a SAS backplane (or period for that matter). The Norco 4020 will do both SATA and SAS...
Click to expand...

There are backplanes that do use SFF 8087 connectors, however it's far more common to use individual connectors per drive.
 
Thank you for the clarification, it does help a great deal!

Numerous newegg reviews emphatically state that this is not a SAS enclosure, are they wrong then? Is anyone using SAS disks in this chassis? (Reason I ask, I have a number of them lying around.)
 
My understanding is that SATA disks are backward compatible with SAS controllers, but SAS disks are not backward compatible with SATA controllers.

Some comments from newegg that have me questioning the SAS support claim,

"Pretty nice in all general areas but wish it had sas like everyone else.."

"I saw the previous reviews that discussed diferent backplanes, but hoped I'd get one w/ SAS. No such luck. I'm still going to use it though. I was toying w/ the idea of including a couple 10k sas drives in the future - but that's out the door now. I mostly wanted SAS to keep the cable clutter to a minimum though. I'll just have to get some sata to SFF-8087 breakout cables (which Newegg doesn't stock)."

"The pictures show SATA and SAS connectors on the backplane, but there are only SATA connectors. I was disappointed to find that the backplane doesn't actually have SAS connectors. If all you need is SATA, I would not hesitate at buying this case."

"This chassis doesn't support SAS, it only supports SATA. There was some mention of SAS in an earlier review, but SAS data connectors have pins on both sides, not just one, and are backward compatible to SATA devices, but SAS devices require the SAS connections and cables for full function and use of the dual-channel redundancy. I give this case 5 stars in spite of its shortcomings, because it fits the task for which I was buying it for, ie. I don't need to stand on it or swap drives often, but getting any other case with this many drive bays of any type would raise alarms with the wife over the "hobby" budget ;)"
 
SAS drives can have pins on both sides of the connector, but it isn't required (those would be dual port drives). This is why you don't go by reviews on newegg. As I said before, this case supports SAS drives.
 
Got it. So what am I missing when using dual-ported SAS spindles, other than the dual port redundancy? I assume I still get tagged queueing etc. as long as I have a SAS controller hanging off the bus.
 
If the backplane supports dual port drives, you pretty much get either redundancy (high availability) or you can cascade the backplanes.
 
I have been research storage systems for about 3 weeks now and am so happy I found this forum. I think from my limited reading that dual ported disks are able to achieve double the throughput according to the plans however this is not implemented yet.

Ref: http://www.google.com/url?sa=t&sour...M-rxiHqNoeo4tMwhg&sig2=zUEYNelIyExnxX0QNzoWPg
http://www.wwpi.com/index.php?option=com_content&task=view&id=853&Itemid=44

I was hoping to find a suggestion on a SAS expander backplane that will be future proof to this eventual functionality. Anyone on here know of anything? (please ignore if too off topic/hijack)

-Garrett
 
You won't get double the throughput because drives are currently not limited by the SATA/SAS bus. The increase in performance will be negligible. Only really useful for high availability...not to mention Seagate is about to release the newer 6gbit SAS drives.
 
Blue Fox,

Each port can support up to 300MB/s correct? I am trying to find a true SAS expander (or SATA multiplier) backplane which will hopefully support multiple drives. After ~3 drives the port throughput will begin to degrade and hence the need for dual porting. I haven't been able to find any backplanes that do this SAS expansion (or port multiplication) yet though. Any ideas?
 
Thanks guys! I had seen that 2.5" backplane before but didn't realize it did that. Awesome. I really was hoping to stick to 3.5" drives though because they are still so much cheaper. That supermicro 2U 12 disk chassis looks awesome for this. If I understand it right with two 1 SAS connection (8087) cards I should be able to support redundant and highspeed links to each drive. With just 1 8087 connection it would be 300MB/s but with 2 it should support up to 600MB/s correct?

These chassis are also cascadable (just heard this term from here) but that means I can expand up to 122 drives by cascading using multiple 826's and only 1 HBA Card correct? or using 2 to get redundancy?

I'm sorry to ask for so much validation... just kinda excited.
 
SFF-8087 cables carry 4 sets of data. One cable will do up to 1200mb/s. You can cascade the cases/expanders, but don't forget that they aren't cheap. One of those is going to set you back about $1000. They aren't really for home use.
 
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