Cables: 4 SATA vs. 1 SAS breakout

[AgedReason]

You could do everyone a large favor if you would re-read the sticky with a critical eye towards my writing and your state of mind, and let me know where you went awry.

Wow! I'd be happy to help. I feel pretty useless going through this forum as I have very very limited knowledge of networking. I'll try to retrace my steps and highlight key statements in the sticky that left an impression.

My method is kind-of all over the place (like those weird pin boards full of random news clippings & string that seem to be in every conspiracy movie). I'll often read a term or concept I don't understand then google it, then search the forum for related material, then go back to the source material. Wash, rinse, repeat. It's not uncommon for me to have half a dozen tabs open on my screens at any given time.

Anyway:

SAS and SATA operate at the same link speeds and use similar cabling.

Okay, the word that stood out to me was similar. Now I realized that could mean anything, but in the context [at least to me] it suggested that they were not completely dissimilar or incompatible.

SATA drives can be attached to a SAS port. The SAS connector is designed to allow attachment of a SATA drive.

This implied to me interchangeability, at least going one direction. I imagined that the SAS port on my X10SL7 would accept both SAS & SATA cables. Now I've never seen an SAS cable, so I have no reliable way of knowing that it won't. I searched, but found nothing conclusive. All the images I found of multilane cables did look different than standard SATA, but I couldn't tell that it positively wouldn't fit. Here's where the word similar came into play.

I thought: "maybe the SAS/SATA port on the MOBO was designed to accept both types of cables in a way I was not familiar with. Otherwise, why would it be an SAS/SATA port? The only way to know for sure is to either get a breakout cable and compare them, or to ask."

SAS drives are incompatible with SATA, however, and a SATA connector will not attach to an SAS drive. Don't try.

Ah! So, "SAS drives are incompatible with SATA however". That to me reinforced the idea that SATA drives are compatible with SAS.

So, to me, this meant I could attach a SATA drive with SAS cables, but I can't connect SAS drives with SATA cables. That would explain why the connectors look similar but not exact - so as to allow connecting an SAS connector to an SATA drive, but prevent connecting an SATA connector to a SAS drive. You know, because "reasons." No problem, I don't even have any SAS drives.

As already noted, single SAS internal cables are very similar to SATA ... and SAS has a special connector used to reduce wiring and aggregate lanes together.

Me: "Reduce wiring? Sounds great. Aggregate lanes? Okay, not sure specifically what that means, but I know what "aggregate" means and I think I know what context "lanes" is being used. I can wrap my head around a 4 in 1 concept. I could go for some of that. And that also might help explain why the connector looks a little different. But I really should hammer out the details. I'm doing waay too much guessing and assuming here."

A multilane connector may be broken into its four individual lanes using a breakout cable. For example, if you get an SAS HBA, it probably comes with one or two SFF8087's on it, but you may want to directly attach hard drives. A breakout cable allows this.


Also, in some scenarios, a mainboard may offer discrete SAS ports which you desire to aggregate into a multilane cable, and so reverse-breakout cables are available as well.

Now, I don't know what an SFF8087 looks like. I don't know that it won't fit on the SATA/SAS port on my MOBO. It looks different to be sure, but not SUPER different; and after all, I recall that the two look similar, not identical. So no surprise there. Also, the concept of expanders were in a separate section from this information about cables and directly attaching hard drives with an SFF8xxx connector. This implied to me that expanders provided additional functionality separate from that of a breakout cable alone. I didn't realize that adding drives were dependent on having expanders.

So my brain read this section as: "If your board has onboard SAS ports, you can directly attach 4 drives using a special multilane breakout cable." Of course, since that's NOT what was written verbatim, the little voice inside me said: "You better make sure that means what you think it means."

After all, there was nothing explicitly stating that what I imagined was correct. And I thought, "If attaching 4 drives to one port using a simple cable was really a thing, there would be dozens of posts about it in dozens of networking sites, right? But so far, I've found bupkis."

That was a warning sign. On the other hand, I hadn't read anything that seemed to directly dismiss the possibility. Maybe that was because it just wasn't a good practice. Or maybe, just maybe, it was because the idea was impossibly idiotic. I didn't know.

________

So I read everything over and over and learned nothing new. In full disclosure, I didn't understand a lot of it, so that probably hurt my comprehension a lot. Maybe a clear explanation was hiding from me. I mean, sometimes it feels like I'm reading a book about "How to speak Greek" written in Greek. Nothing wrong with the book, my ignorance just puts me at a disadvantage. But I really wanted to know about how those breakout cables could potentially fit into my system. So, I figured I ought to just bite the bullet and post the question and maybe the answer would help me now and possibly some other dummy like me sometime down the pike.

The final analysis is that the sticky didn't send me in the wrong direction. It just didn't send me in any direction. I figured my question was simply more rudimentary than its scope (but only you can answer that).

Hope this was helpful.

 

[Ericloewe]

"If attaching 4 drives to one port using a simple cable was really a thing, there would be dozens of posts about it in dozens of networking sites, right? But so far, I've found bupkis."

I understand where this idea comes from. Consumer-oriented publications rarely mention SAS, so it ends up being viewed as this exotic thing only the enterprise market has a use for - somewhat like traditional parallel SCSI - when, in fact, it is more like what SATA should've been, if free of the constraints imposed by ATA and the race to the bottom that the consumer market is.

 

[jgreco]

Wow! I'd be happy to help. I feel pretty useless going through this forum as I have very very limited knowledge of networking.

Of course you're "useless." Everyone starts out useless. If we were born experts, there'd be no need for this forum. The difference between you and me is some number of decades doing this stuff. I come here and hang out because I like to blab about tech.

I'll try to retrace my steps and highlight key statements in the sticky that left an impression.

My method is kind-of all over the place (like those weird pin boards full of random news clippings & string that seem to be in every conspiracy movie). I'll often read a term or concept I don't understand then google it, then search the forum for related material, then go back to the source material. Wash, rinse, repeat. It's not uncommon for me to have half a dozen tabs open on my screens at any given time.

That's ideal :) I spend my days at the opposite end of that, sometimes several hundred tabs open while I dig through the smallest details of things.

Anyway:

Okay, the word that stood out to me was similar. Now I realized that could mean anything, but in the context [at least to me] it suggested that they were not completely dissimilar or incompatible.

This implied to me interchangeability, at least going one direction. I imagined that the SAS port on my X10SL7 would accept both SAS & SATA cables. Now I've never seen an SAS cable, so I have no reliable way of knowing that it won't. I searched, but found nothing conclusive. All the images I found of multilane cables did look different than standard SATA, but I couldn't tell that it positively wouldn't fit. Here's where the word similar came into play.

I thought: "maybe the SAS/SATA port on the MOBO was designed to accept both types of cables in a way I was not familiar with. Otherwise, why would it be an SAS/SATA port? The only way to know for sure is to either get a breakout cable and compare them, or to ask."

So you didn't go totally off track there. Let me ponder that. The problem is that I was contemplating how to describe the difference. I think I probably failed totally, in part because I was trying to avoid endless tangents. But tangents can be good. See, the thing is, there's actually a lot of technical detail that I tried to avoid because it can get TL;DR real quick. Hard to know where to draw that line.

Ah! So, "SAS drives are incompatible with SATA however". That to me reinforced the idea that SATA drives are compatible with SAS.

So, to me, this meant I could attach a SATA drive with SAS cables, but I can't connect SAS drives with SATA cables. That would explain why the connectors look similar but not exact - so as to allow connecting an SAS connector to an SATA drive, but prevent connecting an SATA connector to a SAS drive. You know, because "reasons." No problem, I don't even have any SAS drives.

I have to stop here for a bit. So far, what I've done is some clarifying edits, but I've also added a bunch of links with some pictures that I think are likely to be very useful. Part of the problem with my workflow writing these things has been that I've never had a good way to take pictures and then edit them and then integrate them into the forum discussions without it taking at least 10-15 minutes per picture. I spent a little time "correcting" that issue and now I may be able to get a bit more aggressive in that way.

For example, here's a shot of an actual reverse SAS breakout:

It isn't really horribly hard to stage stuff on the shop bench, and making it easy to go from that to pictures-on-the-forum is, I hope, something that'll be helpful.

I am out of time this morning to work on this, but feel free to comment. I'll slog through the remainder of your previous commentary soon.