LSI/Broadcom/Avago SAS 9400 - SATA, SAS and NVMe in one controller?

[Ericloewe]

https://www.broadcom.com/products/storage/host-bus-adapters/sas-nvme-9400-16i

Apparently, this is one of Broadcom's upcoming storage products and it's an odd combination of features. In a nutshell, it has four SFF-8643/8644 ports (internal/external, depending on -16i vs -16e models). The gimmick is that these can function either as SAS/SATA or PCIe for NVMe (the host-side of the U.2 interface uses SFF-8643, like SAS3).

At launch, each connector supports either a single 4x PCIe 3.0 connection to an SSD or the typical 4x SAS lanes. Future updates will allow for 2x links (presumably over one breakout cable) and support for up to 24 NVMe drives (via PCIe switches, but I get the distinct feeling that there's going to be some lock-in here...).

This feels rather silly, because they're combining a smallish (24-lane) PCIe switch with a largeish (16-port) SAS3 HBA. It would be interesting if this allowed for a single backplane that could take either U.2 devices or SAS/SATA devices, but that's not trivial to achieve - the disk-side connectors are different and U.2 hogs one cable per device, instead of the four per device that SAS does.

 

[Stux]

8 lane card too.

 

[jgreco]

This feels rather silly, because they're combining a smallish (24-lane) PCIe switch with a largeish (16-port) SAS3 HBA.

Makes perfect sense. They're trying to remain relevant by aggressively addressing the weaknesses in attachment. Most midrange systems do not have mega-capacity needs, and simply being able to do a competent job of getting things to and from storage is a significant value-add. When you start looking at things like 1U and 2U servers with a limited amount of disk slots, the challenges in attaching a useful combination of devices becomes apparent.

I'm not saying I like the product or expect it to be wildly successful, but it appears to be an attempt to do some useful things. With the slow evolution away from RAID and towards software-defined storage, not shocking at all...

 

[Ericloewe]

Makes perfect sense. They're trying to remain relevant by aggressively addressing the weaknesses in attachment. Most midrange systems do not have mega-capacity needs, and simply being able to do a competent job of getting things to and from storage is a significant value-add. When you start looking at things like 1U and 2U servers with a limited amount of disk slots, the challenges in attaching a useful combination of devices becomes apparent.

I'd agree - if the two types of devices could work in the same backplane position. Right now, this still relies on a strict allocation of SAS and U.2 ports on the backplane.

 

[jgreco]

I'd agree - if the two types of devices could work in the same backplane position. Right now, this still relies on a strict allocation of SAS and U.2 ports on the backplane.

"... so?"

"... do you have a point?"



The only way we get there is to have people develop the necessary bits. If a controller is available, manufacturers will probably create hardware.

 

[Ericloewe]

After much searching last time I looked up the U.2 drive-side connector, I ended up with the impression that it was similar to the SAS connector, but incompatible with SAS drives. That misconception is what led me to call this controller silly - but, as I've revealed, I was wrong. The draft of the SFF-8639 connector spec (otherwise known as U.2) goes to great lengths to keep the interface compatible with SATA and SAS disks.

Now this makes perfect sense, since Broadcom can sell another insanely expensive part for the backplane that can do SAS (including SATA) and PCIe routing. Since the controller goes for some 500 bucks or more, the backplane is probably going to push this beyond 1 000 bucks - with no chassis or other hardware. Gotta love Broadcom's quasi-monopoly on storage (they're the major source of both SAS expanders and PCIe switches).

 

[jgreco]

Well, it's definitely not "compatible" with SAS drives, as interesting an idea as that would be, but yes there's a lot of interop.

 

[Ericloewe]

Well, I meant that the U.2 backplane connector is compatible with SATA and SAS drives - the rest is up to the backplane. Curiously, the PCIe part is almost completely separate from the existing SATA/SAS pins (except for power, device detection and activity LED and for a still-mythical SAS x4, which carries four SAS links to a single drive instead of two), so the backplane controller (the hybrid SAS expander/PCIe switch) can be little more than its two roles taped together, with the only multiplexing being on the host side, to decide whether to carry SAS or PCIe.

http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_00.pdf

I really wish I'd stumbled upon this document a long time ago. Page 49 shows a comparison of SATA, SAS and PCIe.