The rollout of 12 Gbps SAS drives and other technology will mean performance improvements and new management capabilities. Marty Czekalski, president of the SCSI Trade Association, discussed the
Where does the rollout of 12 Gbps SAS technology stand?
Marty Czekalski: It's just starting up the ramp now, and we've been doing plugfests like the one [from Oct. 21-26] at the University of New Hampshire. We've done a lot of work in wringing out all the bugs. The plugfest went very smoothly, so we're looking forward to a relatively event-free rollout. Our first 12 Gb plugfest was held last year, where people brought their prototypes, and it's usually about 12 to 18 months before end-user shipments start.
Usually, the first place those show up is [in] add-in cards and servers, which is where they're showing up now. If you have a specific need for the performance today, you can get 12 [Gbps] SAS host bus adapters, and there are some 12 [Gbps] SAS SSDs [solid-state drives]. You'll see over the next several months [that] the different OEMs will start offering these as add-ons to their servers.
Today, the servers are shipping typically with 6 [Gbps SAS] on the motherboard. If people want the extra performance, they buy an add-in card for 12 [Gbps]. You'll start to see 12 [Gbps] SAS RAID controllers down on the motherboard starting midyear next year, with the new server shipments typically as a standard feature.
Are there other ways to implement 12 Gbps SAS?
Czekalski: There's a lot of different ways you can implement it. As I said, add-in cards. It'll be down on the motherboard, and you'll be able to plug in 12 Gbps SSDs or [hard disk drives] HDDs. You'll have external storage systems that are connected with 12 [Gbps] SAS as well as Fibre Channel [FC] subsystems that'll be FC on the front end and the back ends will be 12 Gbps SAS to the actual storage devices. People who are rolling out FC or network-connected storage systems are already migrating their back ends to 12 [Gbps] SAS so they can scale out those storage systems on the back end more effectively and into larger configurations.
What benefits will enterprise IT users get from 12 Gbps SAS technology?
Czekalski: It doubles the user transfer rate. The other thing that's coming into play now is more of the host bus adapters [HBAs] will be using the Mini-SAS HD connector, which is a managed connector. It allows a single HBA to accept different kinds of cables. So, you can go with a passive cable, say, up to six or eight meters. You could use an active copper cable by just changing the cable. You can go up to 20 meters with that. Or, you can even go with optical cables up to 100 meters.
In addition, these are managed cables with that connector, so when it's plugged into the system, the system actually knows what kind of cable, what kind of distance it's going. The system can adapt its signaling to optimize it for that particular type of cable. If there's a cable problem for some reason, and the system detects it, it can actually say cable number x, part number y needs replacement. It becomes easier to manage from an IT standpoint.
How was support for that capability built into the system?
Czekalski: It's built right into the connector and cable. The connector on the host bus adapter or on the server is the same in all cases. It's the same low-cost SAS RAID controller or HBA. If you need to go extra distances, you buy a cable that's appropriate. For short cables that are passive, they're very inexpensive. If you need to go 100 meters, you buy an active optical cable, and you plug it in. So, the active components are actually in the connector housing that's on the cable. And in addition to just having the active components, there's also an EEPROM [Electrically Erasable Programmable Read-Only Memory] in there that the system can read that tells exactly what kind of cable it is, its characteristics, part numbers and a bunch of different things.
How do systems based on 6 Gbps SAS work now?
Czekalski: The 6 Gb with the original Mini-SAS connector didn't have any manageability. It didn't have the extra pins to be able to read what kind of cable it was. You had your basic cables for doing six to 10 meters, and then there were some specialty cables and systems built that could take an active copper cable. But there was no way for the system to know exactly what kind of cable was plugged in. With the Mini-SAS HD, there are extra pins for the purposes of providing power to the connector for the active components in both the copper and optical, as well as power to the EEPROM that's in there so the data can be read out.
How will 12 Gbps SAS SSDs stack up performance-wise against PCI Express (PCIe)-based SSDs?
Czekalski: I think you're going to see less extremes and performance differences. And keep in mind that SAS SSDs have different features than a PCIe SSD. The SAS SSDs are dual-ported and connected into a fault-tolerant domain, and all the software is already there and works for failover and high availability [HA]. That feature isn't yet there for PCIe. Yes, they designed the connectors and stuff so that could be done, but that whole ecosystem for being able to do the HA stuff doesn't exist today for PCIe. The other thing that doesn't exist today is the same kind of hot-plug model in PCIe. If you were to go over to most of these PCIe devices and unplug it, you're going to get a blue screen as opposed to a SAS device. SAS is hot-pluggable. You can do surprise plugs and unplugs, and the system doesn't mind it because it's a storage interface that was designed for that. PCIe wasn't originally designed to be hot plugged.
Will users see a substantial performance improvement with SAS hard disk drives?
Czekalski: You will see improvements there with 12 Gb, particularly on 12 Gb HDDs that are hybrid drives that have some flash embedded in them, because the flash can now run at the line rate directly. So, your reads that are coming out of the flash cache on a hybrid HDD will run at the line rate. You'll also get more scalability even if you're just running a traditional SAS HDD on 12 Gb. You can put more of them on the same bus without getting contention. So, you can create large configurations, and you reduce your number of HBAs. You can reduce the number of cables and other things. So, it actually reduces overall system cost and complexity while improving the performance.
How does the future roadmap shape up for SAS?
Czekalski: We've actually already started working on the next generation, believe it or not, the 24 Gb. We've kind of put a stake in the ground around mid-2016 for the first plugfest, so that would mean end-user shipments [around] 2018. The T10 Committee has actually started a new project for 24 [Gbps] SAS, and they had the first meeting. For a lot of the detail, we've had other meetings before that, but it was an entire meeting that was pretty much dedicated to going through the 24 Gb activities.