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Serial SCSI Standard Coming Soon
rchatterjee writes "SCSI is very close to joining ATA in leaving a parallel interface design behind in favor of serial one. Serial attached SCSI, as the standard will be known, is expected to be ratified sometime in the second quarter of this year according to this article at Computerworld. Hard drive manufacturers Seagate and Maxtor have already said that they will have drives conforming to the new standard shipping by the end of the year. The new standard will shatter the current SCSI throughput limit of 320 megabit/sec with a starting maximum throughput of 3 gigabit/sec. But before this thread turns into a SCSI fanboy vs. ATA fanboy flame war this other article states that Serial Attached SCSI will be compatible with SATA drives so you can have the best of both worlds."
Serial ATA Network = SATAN
320 megabytes is about 2.5 gigabits ... which is a lot closer to 3 gigabits than the erroneous 320 megabits figure.
If I understand the title correctly, SCSI = Standard Coming Soon Interface?
If the article meant to say 3GBytes, then how in the world will the PCI *at 64bits and 133MHz, it's 1 GB/sec transfer) bus keep up? Or even RAMBUS memory, which, here says it has a bandwidth of 4.2GB/sec. (So, kinda means you couldn't have more than one SCSI system at a time and get full bandwidth from both.) Now, if you may have to have memory banks for each SCSI component... ick.
I demand a million helicopters and a DOLLAR!
Sure, this definately looks like it could be a great setup: fast, and compatable on multiple systems. But how much will this technology cost? Standard, run of the mill IDE hard drives are about a dollar per Gig. Regular SCSI is a few times higher, especially as drives grow in size. This will be a great advantage if the price range is in the middle of the range, but I doubt that. Now, this won't matter to those with plenty of money to burn on their servers, but would that added price be worth the new types of hard drives? I still don't even see a huge advantage to going Serial ATA right now, so this seemingly good idea could just be another good idea that won't pan out for most users.
take off every sig for great justice
Hopefully this will eventually lead to the elimination of the distinction between ATA and SCSI interfaces. Already the feature distinctions between the two are blurring, hopefully soon the interface will be the same and people will just decide whether they need fast or cheap drives. That would improve the quality of desktop class drives and lower the price on workstation/server drives, as well as make system managment a bit easier.
To reduce crosstalk between the wires so that you can run at faster speeds. Indeed, the "rounded" IDE cables often reduce performance by 5% or so. We're getting better at data throughput though, so we can use serial technologies and actually get faster transfer rates. Good riddance to ribbon cables :P
>Why not simply roll the ribbons up into cables?
Impedance, crosstalk (mentioned) and price.
It takes seconds to crimp a ribbon cable. Cheap and easy. You can even do it yourself!
Taking a bunch of twisted pair wires (which is what would be required to keep the impedance and crosstalk bearable) and soldering them onto connectors individually takes a lot more effort, and therefore costs more.
Not to mention fabbing individual strands of insulated wire and twisting them together costs more than running 5 wires parallel to each other and simply coating them all at the same time with PVC.
If you could be told what you can see or read, then it follows that you could be told what to say or think - BoC
I've only paid attention to HD controllers for the last couple of years or so. But I'm starting to wonder if we're seeing a pattern here. "We'll make everything more efficient by making it serial, and then years later when that's not enough we'll make it paralell to send even MORE data through!"
Anybody think we'll have a massive paralell trend in a few years?
SCSI: Small Computer Systems Interface
descended from
SASI: Shugart & Associates Systems Interface
STOP . AMERICA . NOW
Firewire is low end consumer product...even with its successor (which is taking longer than expected to ship) running at 800Mbits/s (100 Megabytes/second) it falls short of current SCSI technology running @ 320MB/s. As such there is no one who would seriously consider firewire for a large scale server handling many gigabytes/terabytes of data. Firewire is just too slow of a bus for big needs, but does fills its convenience needs in the consumer market. Everything has it's own niche... that's why heavily marked up servers/mainframes/supercomputers still exist instead of cheaper home machines which just can't fill the requirements.
That doesn't matter. Almost everything else in the post is in error. SCSI already has a serial interface standard (and has for a very long time.) -- ever heard of Fibre Channel or Firewire? SATA and SSCSI compatiblity? F***ing duh! What do you think ATAPI is? The SCSI command protocol moving in packets across an IDE physical interface.
I don't know what stupid scheme they are trying to create here -- interface-wise. SATA is a point-to-point configuration. SCSI has always been a bus configuration. If they go the p-t-p route, then it depends on the controller to be able to support the device on the other end -- SCSI crossing the pyhical interface or IDE/ATA/ATAPI crossing it. (Think parallel port ethernet dongle.) I'll have a hard time accepting p-t-p SCSI.
If they want to make SCSI more attractive, they should stop significantly over charging for the technology. They can bulk test "desktop" SCSI drives just as cheaply as IDE drives. They all use the same servo assemblies -- and in some cases, the same basic interface logic (obviously with different microcode.)
FYI - signals do not travel at the speed of light. Somewhere around 50-60% the speed of light in most types of cable.
Overcoming the differences in arrival time of signals in a parallel cable is not significantly more difficult than handling clocking (and maybe clock recovery) and buffering and serial-to-parallel conversion on a serial interface.
The main reason that parallel interfaces were popular years ago when things like SCSI were established was the electronics at the time just weren't very fast. The 74LS00 family logic that SCSI and parallel printer ports were designed around had a maximum clock rate of about 30Mhz. Add in margin for cable noise and distortion and 5-10Mhz was absolutely the most you could manage through any distance. So, if that wasn't fast enough for what you wanted to do, you used more wires in parallel.
These days, it's relatively easy to put multi-gigahertz logic onto chips, and the fewer wires in a cable and connector, the cheaper, so serial wins.
One detail is that SAS is now point to point, just like SATA, and not a bus, but they also indicate that there would be boxes to split a single connection to a bunch of devices, sort of like network hubs. The protocol addresses 128 devices. It isn't clear whether a hub could have SATA devices hooked to it, or if that would require 1 serial channel per device from the host adapter. That is what I understood to be the case for SATA (need one port for each device, no hubs or sharing). The most important protocol difference should be that SAS is still multipoint, even if the connections are point-to-point, so both hosts and adapters need to arbitrate for the bus, while SATA hosts adapters just send out commands and data and wait for the drive to respond on the reverse channel.
It wouldn't surprise me if devices eventually just supported both protocols, and maybe even auto-sensed the type of adapter on the other end. By the time these interfaces get common, I expect the cost differences to be negligible, so It begs the question of why SATA would survive. Because the cost differences are going to be sunk into the chipset designs with almost no marginal cost differences, both system and drive makers will probably save more by reducing the size of their product lines by having one product for both.