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| SAS 1.0/1.1 | SAS 2.0 | |
| Features | Preserves legacy SCSI SATA compatible | 3 Gb/s compatible Improved signaling Zoning management Improved scalability |
| Storage Features | RAID 6 Small form factors HPC High capacity SAS drives Ultra320 SCSI replacement Choice: SATA or SAS Blade servers | RAS (Data Protection) Security (FDE) Clustering Larger Topologies SSDs Virtualization External Storage 4K sector size |
| Line Rate and Cable Throughput | 4 x 3 Gb/s (1.2 GB/s) | 4 x 6 Gb/s (2.4 GB/s) |
| Cable Type | Copper | Copper |
| Cable Length | 8 m | 10 m |
Source: www.scsita.org
Expander Zoning and Self-Configuring Expanders
Edge expanders and fanout expanders are nearly history. This is often attributed to updates in SAS 2.0, but the reality is that SAS zoning, which predates 2.0, was already paving the way to eliminating the edge/fanout distinction. Admittedly, zoning is usually implemented in a vendor-specific, rather than industry-standard fashion.
In a nutshell, various SAS zones can now be deployed across shared delivery subsystem hardware. This means that targets (drives) in a storage appliance can be accessed by various initiators through the same SAS expander. Domain segmentation is taken care of through zoning, and access is managed in an exclusive, non-shared manner.
With device discovery moving from the initiator to the SAS expanders, this allows expanders to self-configure their functions. Discovery time on large topologies can thus be reduced and zoning could be standardized to get rid of proprietary solutions.
Doubled Link Throughput
SAS 2.0 mandates that the bandwidth per port doubles, from 3 Gb/s to 6 Gb/s. Quad links, which are typically used for wide ports, go from 1.2 GB/s to 2.4 GB/s. And since SAS HBAs typically offer eight ports organized into two wide ports, the effective maximum throughput stands at 4.8 GB/s.
PCI Express 1.1 then becomes a bottleneck because the popular x8 link width only offers 2.0 GB/s (250 MB/s per lane each way). As a result, all upcoming SAS 2.0 hardware will also be based on PCI Express 2.0 host interfaces, doubling the available bidirectional bandwith to the host to 4.0 GB/s.
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Now I like this, can't wait to see it implemented on EMC & IBM platforms. And on the servers side I'd like to see some numbers on spec's and performance. Good article Patrick Schmid and Achim Roos! Next.... benchmark 2.5 vs 3.5 on enterprise systems and low budget small business ....yes???
SCSI is still not dead?!?!?
Joking aside, I wonder if any motherboard manufacture like ASUS will get this on their high end WS models (see P6T WS). And I wonder if they will make any SSDs using this for the server sector.
[citation][nom]Shadow703793[/nom]SCSI is still not dead?!?!? citation]
no its not -- its a long death cause most scsi drives run forever. I have a bunch of scsi drives running on my systems at home and as much as Id like the performance boost of SAS or even Sata, the things just wont die.
but 6g/b SAS looks to be the next upgrade step
6Gb for SAS is kind of pointless considering SAS drives only peak 100MB
On this page (http://www.tomshardware.com/reviews/sas-6gb-hdd,2392-8.html), I see that you stated "SAS 1.1 at 3 Gb/s (300 MB/s)"
Well this has always confused me. If SAS 1.1 is 3 Gb/s, that would be 375 MB/sec (3 x 1000 to convert to 3000 Mb/sec and then 3000 \ 8 to convert to 375 MB/sec.)
On the SAS Wiki site (http://en.wikipedia.org/wiki/Serial_Attached_SCSI) it shows 3 Gb/sec. However on the list of device speeds Wiki site (http://en.wikipedia.org/wiki/List_of_device_bandwidths) it shows 2.4 Gb/sec with a 300MB/sec. The only maximum that appears to stay the same is MB, which is 300. So is it really 2.4 Gb/sec or is it 3.0 Gb/sec really for SAS 1.1?
Thanks!
@kittle -- Not to mention that SCSI is a protocol, not just a physical/electrical interface. SAS simply changes the physical/electrical interface, but the good old SCSI protocol is still in there (just like SATA still has ATA underneath).
@falchard -- No, it's not pointless. A dedicated controller channel for every drive would be prohibitively expensive for large drive arrays (not to mention the cabling nightmare), which is why SAS (unlike SATA) allows for more complex topologies, not just point-to-point. When you put multiple drives/expanders on a channel, you can quickly hit SAS bus speed limits.
@rhodenator -- SAS (like SATA) uses 8b/10b encoding. That is, 8 data bits end up as 10 bits on the wire (typical of high speed serial buses), so: 3.0Gbs wire * 8/10 encoding = 2.4Gbs data = 300MBs data.
I bet the hardcore gamers are drooling at the prospect of SAS 6Gb/sec. Too bad they'll have to wait.
Actually, LSI was not 1st to market w/ 6g controllers. ATTO Tech was shipping their H6xx 6G HBAs months ago based on the PMC Sierra chip. Also HP has been shipping their 6G RAID controllers - P212 & P410 (also PMC Sierra chip) for a couple of months also. Granted LSI is the industry leader w/ SAS but has stumbled in execution of releasing 6G product.
Actually, LSI was not 1st to market w/ 6G SAS controllers. That distinction goes to ATTO Tech with their H6xx 6G HBA line up and HP for their 6G RAID controllers - P212 & P410. All of these are based on the PMC Sierra chipset. LSI has been stumbling to get 6G products out the door.
re: rhodenator. As mentioned in the article; 8b/10b encoding means that 8bits data is encoded using 10bits accross the link. 3000Mb/10b = 300MB. Command and control overhead and processing delay further limits real world performance to about 270MB/s. I think someone managed over 580MB/s using the new 6Gb/s signalling and more data per transfer to reduce overhead (was that using SATA or SAS ?).
re: falchard "..kind of pointless.." NO.
"Build it and they will come". You have to start building the infrastructure and plan for the future otherwise it's pointless making the drives go faster. I want a server that in a few years time can take additional drives or replacements where performance boost is not nullified by slow IO bandwidth.
It will take 12months after the standard's release to be more common as HBA, motherboard and drive designs are refreshed.
SATA is no longer a 1-to-1 link and burst bandwidth is close to current limit.
600MB/s means enough bandwidth to aggregate 4 of today's SAS HD per SAS port or maybe 2 SSD's. Within 2 years a single HD will exceed current limit and within 1 year SSD's will reach the new limit.