Serial SCSI Standard Coming Soon 328
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."
Bits? Bytes? Whatever! (Score:1, Informative)
bits vs. bytes (Score:5, Informative)
320 megabytes is about 2.5 gigabits ... which is a lot closer to 3 gigabits than the erroneous 320 megabits figure.
Re:Mbit != MByte (Score:2, Informative)
U320 SCSI (Score:2, Informative)
U320/LVD SCSI is capabable of 320MB / sec not 320mbps.
3gbps ~= 300MB/sec. therefore it would not be be quite as fast as U320 SCSI.
Naturally 320MB/sec is the theoretical max bandwidth for the SCSI bus not the individual drives in the SCSI chain.
Live long and prosper
For more info (Score:3, Informative)
http://www.lsilogic.com/products/islands/sas_isla
Re:SASCSI (Score:5, Informative)
Re:SASCSI (Score:5, Informative)
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.
Re:Is this a trend? (Score:5, Informative)
Re:Parallel Interface? (Score:3, Informative)
Re:Ok, So I've noticed a couple of corrections. (Score:2, Informative)
Re:Parallel Interface? (Score:5, Informative)
descended from
SASI: Shugart & Associates Systems Interface
Re:why is serial better? (Score:2, Informative)
I think the problem(s) come when you have to take into account keeping parallel lines in synch with one another, accouting for lost bits, and breaking down/putting back together all the information at either end. This all adds up in overhead for a parallel connection, where a serial connection just lets the information go through the line with little or no pre/post processing or synching to worry about.
Re:Ok, So I've noticed a couple of corrections. (Score:4, Informative)
Re:Firewire? (Score:5, Informative)
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.
Re:Benefits of SCSI? (Score:2, Informative)
Re:Benefits of SCSI? (Score:2, Informative)
Most board manufacturers include only two IDE channels because that's how many are generally built into north-bridge chipsets. The Abit boards mentioned above use an additional Promise HPT374 chip to provide FOUR extra IDE channels, for a total of TWELVE IDE devices, altogether.
If you want more IDE devices than your board supports natively, you can just buy PCI cards that have more IDE channels. Promise, SIIG, and Highpoint all make really cheap cards that have an extra two channels, or four more devices.
SCSI limitations are similar. You only get 15 devices PER BUS, but you can add as many devices into your system as you have PCI slots and IRQs for. You can buy an Adaptec 29160 card (dual busses) and plug 30 hard drives into it. Buy four of them, and can have more than 100 drives.
Re:why is serial better? (Score:1, Informative)
Re:Ok, So I've noticed a couple of corrections. (Score:2, Informative)
http://www.hypertransport.org/
11.
Question:
At what clock speeds does HyperTransport(TM) technology operate?
Answer:
HyperTransport(TM) technology devices are designed to operate at multiple clock speeds from 200MHz up to 800MHz, and utilizes double data rate technology transferring two bits of data per clock cycle, for an effective transfer rate of up to 1,600Mb/sec in each direction. Since transfers can occur in both directions simultaneously, an aggregate transfer rate of 6.4 Gigabytes per second in a 16 bit HyperTransport(TM) I/O Link and an aggregate transfer rate of 12.8 Gigabytes per second in a 32-bit HyperTransport(TM) I/O Link can be achieved. To allow for system design optimization, the clocks of the receive and transmit links may be set at different rates.
----
For the pentium4:
133MHz Quad Pumped (533MHz effective) allowing access to up to 4.2GB Bandwidth
But I guess that most of the trafic is mem-hd
or hd-mem and thus does not nead to go trough
the cpu, I think the latest alphadesign was
to have 8 rambus chanels giving plenty of
bandwith
Yup -- post is wrong, eds please amend (Score:3, Informative)
Existing SCSI is 320Mbps*8bits/byte = 2.5Gbps.
Moving to 3Gbits is evolutionary, not a huge jump.
I'm wondering what's going on here too -- WTF happened to Firewire? I remember thinking that everyone would be using it as a universal high bandwidth data bus, and for some reason it doesn't seem to be happening.
A couple of notes (Score:4, Informative)
First, SAS uses a point-to-point topology similar to Serial-ATA instead of a shared bus like SCSI. This means each drive has access to full bandwidth, not just one (the bottleneck being the card itself).
Second, according to the SAS working group, SAS comes in three speeds; 150, 300 and 600 MB/s. I'm not sure where that 3 Gbps figure came from.
Third, unlike Serial-ATA or parallel SCSI, SAS is full duplex like fibre channel. This should have some interesting effects on latency.
Fourth, SAS uses the same physical connector as Serial-ATA and in fact can use Serial-ATA drives in legacy mode.
IBM's had this for several years, it's called SSA (Score:3, Informative)
coward
Re:Does SCSI now compete with firewire2 ? (Score:1, Informative)
Where have you been ? I've been using 1000BaseTX ethernet for over a year. Right now I would only buy a machine with a GigE port. The switches are still a little pricey but they will come down.
10 Gbit was ratified last year. See here [ethermanage.com]. It's only multimode fibre though.
Re:Benefits of SCSI? (Score:3, Informative)
For desktops, not really. For server, yes. SCSI, due to (generally) lower latencies, higher rotational speeds and a smarter interface destroys IDE in high-load multi-user style scenarios (lots of random reads & writes all over the disk). Very few (if any) desktop users generate the sort of usage patterns that allow SCSI to shine, so on the desktop it has little advantage (particularly taking into account the cost).
Most people who say SCSI gives them a good boost on their desktop machines are usually comparing quite new SCSI drives to quite old IDE ones, are dealing with poorly-configured IDE setups (more than one device on a channel) or are using an older, slower machine (probably with a crappy IDE controller). For the vast, vast majority of users (and that includes high-end users) SCSI offers little benefit.
Re:SASCSI (Score:2, Informative)
I have a 10M SCSI ribbon, and each pair is twisted. I think the main reason for ribbons inside the box is so you can crimp on a connector wherever you want. Oh, and in a Sparc20, the internal SCSI cable isn't a ribbon, it's a cable from the motherboard right up to where it connects to the disks, cable again to the CDROM.
So, IMO, there's no reason it can't be a ribbon, except for the convenience of crimping connectors wherever you want.
Ummmm.... (Score:3, Informative)
That's already ~2.5Gbits/sec.
And isn't there a SCSI640 working group, too?
-psy
No SAS drives on SATA (Score:3, Informative)
http://www.snwonline.com/whats_new/sas_and_sata
The article states that the SAS drives won't work on a SATA channel, but SATA drive will on the SAS.
I wonder if mobo makers like ASUS, ABIT, MSI and the likes will choose to have SAS ships on the mobo instead of SATA, as a performance feature?
Lets hope so it would sure open a lot of option for upgrading a PC over time.
Re:why is serial better? (Score:4, Informative)
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.
Re:I'm so confused. It's not Firewire? (Score:1, Informative)
Re:bits vs. bytes (Score:3, Informative)
You can already get USB2 and FireWire cards that can do high speed transfers simultaneously on several connectors, and if this really takes off, there is no reason why you couldn't have a card with 8 or 16 independent channels (ultimately, of course, it gets silly because PCI can't keep up anymore).
SATA vs SASCSI (Score:5, Informative)
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.
Re:Mbit != MByte (Score:1, Informative)
If you bothered to read the second article you'd know that SATA and SSCSI will have compatable physical interfaces, no adapter needed. Who cares if ATAPI is SCSI over a IDE physical interface if i can't plug one into the other without spending more money for a adapter of some sort. Plus if you checked out the specs you'd know that SSCSI is going to be faster than both fibre channel and firewire, niether of which have the physical interface compatability of SSCSI with SATA. next time RTFA.
Just some info about the cables (Score:3, Informative)
I for one will be doing my best to hunt down a supplier which makes precise lengths so I can have mine cut to size as they aren't as easy to route as a ribbon cable (seriously!)
Plus if you have 6 devices that's SIX cables in the box instead of 3,... - one of the small shortcomings of SATa
(when I first heard about it, I was under the impression it dasiy chained with an "in" and an "out" port - boy did I think that was FANTASTIC... but I was sorely disapointed when I discovered I was incorrect)
Re:bits vs. bytes (Score:1, Informative)
SATA, etc. is different, but that's neither here nor there since you're talking about the current implementation - okay, some bizaaro implementation that would require all-new silicon on both drive & controller for all these extra connectors.
BTW, ultimately on an intelligent bus, you can do drive->controller->drive transfers without involving the CPUPCI bus. If SATA is implemented like regular ATA then yes, the PCI bus is going to get saturated (Intel works very hard to hobble standards so they're CPU-bound as much as possible, thereby increasing sales of high-end CPUs).