SATA and SAS. Can I mix? Should I go with SAS?

[katit]

I'm building home NAS, it will be SM case with SAS2 backplane. I already have some SATA drives I'm going to put into one pool. But I'm looking to build new pool with newer and potentially better drives. I was thinking WD Reds

But now I see I can get SAS drives for very close price. What will it give me if I go with SAS? Will the be faster? More reliable? Will this pool conflict with other SATA pool?

I plan to use FreeNAS/ZFS with those drives.

 

[audio catalyst]

more reliable definitely, beter protocol.. dual links.. and yes you can mix..
for speed add more memory and or ssd's

 

[T_Minus]

If it's the same price go for SAS but just know you should use SAS in the rest of the spots too, at-least that's what I've read over and over and is the reason I avoided it for my home. If you need a new drive new SAS is $$, and used SAS on forums are much more rare than SATA.

 

[katit]

If thats true and I can't mix them on a same backplane - then it's no go for me as I have some SATA drives already. But IF I can use them on same backplane but in separate pools - it might work for me. Do you have any links to this problem? I don't like to test it myself I want them more out of curiosity as I probably won't even know a difference in my application...

 

[acmcool]

Preferred is not to mix them...
Either go Sata or SAS...
Nearline SAS only benefit is better protocol...It same platter/mechanicals as SATA drive

 

[jasonlitka]

You should not mix SATA and SAS drives on the same expander or on the same controller if directly attached to your HBA. If you absolutely need to then you should use interposers on the SATA drives.

 

[coolrunnings82]

I have heard this for years. What is the reasoning behind it? Does SAS handle things better if a drive goes nuts and keep the storage system stable or something?

 

[jasonlitka]

I have heard this for years. What is the reasoning behind it? Does SAS handle things better if a drive goes nuts and keep the storage system stable or something?

Most SAS drives come with Enterprise-oriented firmware (TLER, optimized for multi-user, random IO) but that's not necessarily exclusive to SAS. The real reasons are more longevity, most are warrantied for 5 years, and they're dual-ported so you have redundant paths, or can attach them to two servers for HA.

 

[coolrunnings82]

So basically no biggie to mix long as it is WD RE series and the like just no consumer drives...

 

[jasonlitka]

So basically no biggie to mix long as it is WD RE series and the like just no consumer drives...

No, as I said before, you cannot mix them without interposers or a separate controller. Odd things will happen, if it works at all (some controllers block it if the condition is detected).

 

[coolrunnings82]

I have that configuration in use in a few places and never ran into issues with it. Wonder which systems are more/less tolerant of that configuration.

 

[T_Minus]

im curios too

 

[neo]

Most SAS drives come with Enterprise-oriented firmware (TLER, optimized for multi-user, random IO) but that's not necessarily exclusive to SAS.

I agree. TLER is also very desirable - if not a requirment for RAID configurations. The WD Re drives have this in their SAS and SATA variants.

 

[jasonlitka]

I have that configuration in use in a few places and never ran into issues with it. Wonder which systems are more/less tolerant of that configuration.

im curios too

SAS and SATA disks use different signaling levels (~1V vs. ~0.5V). A SAS controller can do either, but not at the same time. The higher voltage used in SAS allows for longer cable lengths than SATA (10m vs 1m) & passive backplanes (ones without expanders baked in). If you have any SATA devices attached then everything on that controller will use SATA signaling levels and you may experience issues with drives dropping out.

If you are using expanders then this only applies to drives attached to the expander, not all the expanders attached to your root controller.

 

[coolrunnings82]

Awesome! Finally got a technical reason for it being a bad idea. Everyone always says so but I have never heard a real reason why. Thanks for taking the time! I appreciate it!

 

[jasonlitka]

... to continue, using Interposers on a SATA drive allows them to communicate with a SAS controller using SAS commands (though not all will work as they would with a native drive), SAS signaling levels, and it will add the dual-ported accessibility necessary for HA environments.

 

[PigLover]

Awesome! Finally got a technical reason for it being a bad idea. Everyone always says so but I have never heard a real reason why. Thanks for taking the time! I appreciate it!

And pay attention to the details. You only need the higher SAS signaling voltage if you are using longer cable runs. If everything is inside a single chassis, on a single backplane and with the MB inside the same box the SAS drives will be fat, dumb and happy at SATA signaling levels.

For most people here, in most of the configurations we discuss here, SAS and SATA mix happily. If you've got a full 42U rack full of drive enclosures daisy chained you'd be an idiot to be using SATA drives anyway...

 

[jasonlitka]

And pay attention to the details. You only need the higher SAS signaling voltage if you are using longer cable runs. If everything is inside a single chassis, on a single backplane and with the MB inside the same box the SAS drives will be fat, dumb and happy at SATA signaling levels.

For most people here, in most of the configurations we discuss here, SAS and SATA mix happily. If you've got a full 42U rack full of drive enclosures daisy chained you'd be an idiot to be using SATA drives anyway...

Eh, maybe. A 4U chassis with direct connections and no expanders may not reliably work at SATA voltage. People always forget about the trace length of the backplane, as well as the loss from the extra cable connection. I know, I've had a box like that...

 

[PigLover]

Not to be argumentative, but if you've got a backplane with 1 meter plus trace lengths then I'd suggest you've got a defective backplane...

 

[jasonlitka]

Well no, of course not, but it's very common to need a 2ft cable from the HBA to the backplane. That, plus trace, plus the extra connector, can put you out of spec.