So why change the cables?

September 24, 2013

Adaptec 7 and 8 series controllers have moved to the new mini-SAS-HD (high-density – codename 8643) cable as opposed to the previous “mini-SAS” (codename 8087) connector of the 3, 5 and 6 series controllers.

Why?

The older 8087 has served its purpose and been a very good, robust, reliable and fairly trouble-free connector for quite a few years. So why change it? There are technical and physical reasons why we have done this … read on for the explanation …

Background point: RAID processors were, and have been up until the Adaptec 7 series, 8 port on chip. This means that the series 6 controller for instance, and all of Adaptec’s competitors, only have 8 native ports on their controller to connect to devices. All Adaptec’s 7 series controllers however have 24 native ports on the chip, which means we need more than 8 physical ports on the card to make use of those ports.

The mini-SAS (8087) form factor fitted fairly well on RAID cards because it connects 4 ports from the RAID processor to a single cable. Consequently 2 connectors on the card utilized all the ports on the RAID processor. This worked well for a long time, and created a simple “standard” that RAID cards used because everyone in the industry was working with 8-port chips and 2 connectors. Like any technology, if everyone does the same thing for a while then it becomes a de-facto “standard”.

Accessing more than 8 devices has always required a work around with this style of card as 8 devices is the physical limit. That work-around comes in the form of an expander. That expander can either be on the backplane, connecting an 8-port chip to more than 8 drives, or it can be physically mounted on the RAID card as in the case of the 51645 3gb/sec card.

While expanders work well in most cases, there are situations where they are undesirable – especially in the performance end of the storage spectrum, and specifically when SSDs are utilized. They inhibit performance in SSD environments – and while that was not a problem a few years ago, the SSD has invaded the storage space and are found in all manner of systems these days.

External factors …

Hard drive vendors are focused on 2.5” drives. They promote these as their performance products (even in spinning media), while they promote the 3.5” drive as the “capacity” device. With the proliferation of 2.5” drives, the 2U chassis is starting to become a dominant form factor from the chassis vendors – because it’s big enough for the computing requirements and you can fit up to 24 2.5” drives across the front of a 2U chassis.

So between the drive vendors and chassis vendors, 2U is becoming mainstream, and bringing with it the need to connect more than 8 drives in a small, confined space.

Now that can be resolved with expanders on the backplane – agreed. However, taking into account the previously-defined performance issues with SSDs and expanders, and the fact that SSDs are 2.5” and tempting to put in these boxes in one way or another, and it becomes highly desirable to connect all those drives “without” an expander in the equation. Especially when taking into consideration such technologies as SSD caching, and Hybrid RAID, SSD is becoming a pervasive force in storage in one form or another … and you certainly want your storage infrastructure to make full use of that performance and not hinder it (especially because you paid so much for those drives).

So …

Put all that together:

  1. SSD becoming commonplace
  2. Chassis vendor pushing for 2U 2.5” form factor
  3. Drive vendor pushing towards 2.5” form factor
  4. Expander technology inhibiting SSD performance
  5. A RAID card with 24-native ports on the processor
  6. The desire to fit all that in a low-profile product to fit in 2U chassis

The result is the need to put more than 8 direct connections on a low-profile RAID card. Only problem is that this can’t physically be done with 8087 connectors – they are too big. So Adaptec looked to the future, and looked at the industry-standard connector being introduced in the very near future for the 12gb SAS standard – the mini-SAS-HD 8643 connector.

The 8643 allows us to fit 4 connectors on a low-profile card (16 native port connections). If we want more (24) then we need high-profile because even with the efficient size of the 8643 it’s just not possible to fit 24 port connections on a low-profile card. So we used the 8643 and created a range of the world’s highest density RAID controllers in the process.

Ramifications

Technically – none. Logistically … hmmm. Yes we had to create a new range of cables to connect the 8643 on the controller to the 8087 on the backplane etc, but we made sure we stuck to standards, and that the cable vendors of the world have gone along and created plenty of alternatives to using Adaptec cables (though of course I’m always going to recommend to use our cables).

Reality

System builders have always had to source cables. Either from the card vendor, and often from other 3rd-party manufacturers. With the introduction of the 8643 connector it has become necessary for people to go through the logistics of sourcing new cables (or learning new order numbers), but we believe the benefits associated with the increased density of connectors and the ability to bypass expanders in many more configurations than previous are worth the pain that we have all gone through in learning these new technologies and their associated part numbers :-)

Ciao
Neil

 

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