Promise Pegasus R6 & Mac Thunderbolt Review
by Anand Lal Shimpi on July 8, 2011 2:01 AM ESTFinal Words
There are really two things that need concluding in this article. We'll start with the Promise Pegasus R6. Without a doubt this is the highest performing external enclosure you can get for your 2011 MacBook Pro or iMac. Even using lowly mechanical hard drives you can get absolutely amazing sequential performance out of the R6. In its beefiest configuration you get 10TB of storage that you can readily access at over 600MB/s. For a MacBook Pro or iMac user that does a lot of HD video work, this amount of high speed storage is just unheard of. The big tower guys have always been able to piece together beefy RAID arrays, but now you're able to get that sort of an experience in a more compact computing device.
I'd love to see Promise offer a version of the Pegasus with SSDs instead of mechanical drives. If Promise didn't want to retool the Pegasus' design it could come in the same chassis, but it'd be really nice to see an even smaller form factor chassis designed exclusively around the 2.5" form factor. I've already shown what four high speed SSDs can do in the R6's chassis. You obviously don't get the capacity but I suspect there's a class of users out there that needs more than what a MacBook Pro can offer with its internal drive bays, but doesn't quite need 10TB of storage.
The Promise Utility that comes with the Pegasus is nice but I found it slightly temperamental at times. I almost feel like we're another couple of software/firmware revisions away from a more polished solution, although admittedly I didn't encounter any issues when I was just using the device as configured.
The biggest drawback to the Pegasus is its price. At $1999 fully loaded, or $999 for an entry level 4TB R4 it's just a very difficult device to justify. I suspect if your work depends on it then you'll have no problems spending the money, but it is a very niche product as a result. I would like to see Promise or someone else offer a barebones Thunderbolt chassis for those users who need this sort of performance but at a better price point. I can understand the price premium for Thunderbolt, but at these prices the technology is simply out of the reach of too many who could honestly use it.
Which brings me to the next topic of discussion: Thunderbolt. The interface is fast, there's no doubt about that. With the right drive configuration I had no problems pushing 8Gbps over the PCIe channel while sending another ~7Gbps over the DisplayPort channel to a 27-inch monitor. It's clear that Thunderbolt has what it takes to really enable more users to migrate from big desktops to high powered quad-core notebooks. The interface effectively solves the high speed local storage issue.
I'd love to see Apple get really aggressive here and offer a Cinema Display with two Thunderbolt ports, more USB ports, Ethernet and audio out. Then MacBook Pro users would only have to run a single Thunderbolt cable + power to their notebooks when they're docked at a desk. I'd also like to see full-speed performance when used in Target Disk Mode. Thunderbolt could become the new defacto way to quickly migrate data between Macs.
I am concerned that we may run into bandwidth limitations in the not too distant future. If we can already push 5 - 8Gbps of data on a single channel, what happens when you run Gigabit Ethernet and USB over Thunderbolt as well. For high end users, I see a definite need for faster signaling or multiple Thunderbolt ports.
I also have concerns about cable costs and widespread adoption. For Thunderbolt to really take off we need to see tons of products that support it. Intel's Thunderbolt controller IC can't be cheap, so I am curious to find out if more companies will give Thunderbolt a try. I believe cable costs can be prohibitive, but today device costs are the bigger concern.
Intel already announced that we'd see Thunderbolt support in Ivy Bridge designs next year so it may be at least one more year before we see just how much market potential Thunderbolt has. While I'm happy that Apple is championing the standard, Thunderbolt really needs widespread industry support to make an impact.
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etamin - Sunday, July 10, 2011 - link
hmm, I think I'm missing something here. Are you saying that the new MBPs have 12 lanes to the dGPU because 4 have been borrowed (on demand?) by the TB controller? or does the PCH has its PCI lanes? if so, how many? Thanks for the reply.repoman27 - Sunday, July 10, 2011 - link
Anand explained it in his review of the mid 2011 iMac, here: http://www.anandtech.com/show/4340/27inch-apple-im...etamin - Monday, July 11, 2011 - link
I see...I never noticed the PCH/SB always had PCI lanes of its ownrepoman27 - Saturday, July 9, 2011 - link
"At the end of a Thunderbolt chain you can insert a miniDP display, currently the only option is the 27-inch LED Cinema Display but in theory other panels that accept a miniDP input could work as well."Any DisplayPort enabled display will work, and there's plenty of those. You just need to use an asymmetrical cable. Just like you don't need a display with a mini/micro HDMI port to use the mini/micro HDMI out on the devices that have those. Or a PC with mini/micro USB ports.
mAxius - Sunday, July 10, 2011 - link
intel and apple will have thunderbolt the rest of the planet will have external pci express and usb who will winhttp://www.eetimes.com/electronics-news/4217190/PC...
Focher - Sunday, July 10, 2011 - link
According to that article, their standard is due for mid 2013. It's slower than TB and it's not even real. They've just announced plans to make something.repoman27 - Sunday, July 10, 2011 - link
“I'm not entirely convinced that we're limited by Thunderbolt here either - it could very well be the Pegasus' internal controller that's limiting performance.”I’m pretty sure what you’ve gone and done here is bumped into the ceiling imposed by the CPUs in those Macs only supporting a PCIe maximum TLP payload size of 128 bytes. You achieved a little better than 80% of the total 10 Gbps bandwidth available on one Thunderbolt channel in actual data throughput, which is surprisingly good. Even though that bandwidth is exclusive of PCIe’s normal 8b/10b encoding overhead, there’s no getting around the additional overhead inherent to any packetized protocol. A Thunderbolt controller paired with a northbridge that supports 4096 byte payload sizes could theoretically achieve around 99% of the full 10 Gbps.
You’ve also shown that one device using a single Thunderbolt channel can use > 50% of the bandwidth of the 4 PCIe 2.0 lanes connected to the Thunderbolt controller. Thus if you connected one 4-drive SF-2281 Pegasus R6 RAID-0 to each of the Thunderbolt ports on the 2011 iMac, you still shouldn’t expect more than 12,833 Mbps combined throughput.
The Target Disk Mode results are disappointing, although you’re always limited to the speed of the slowest drive that you’re transferring to/from. You didn’t mention what the iMac was packing, but if it’s still just the 1 TB 7200 RPM Seagate that was in the model you reviewed earlier, that would be the limiting factor. Did you check to see what you could pull using FireWire Target Mode between the two?
“simply displaying an image at 60Hz on the 27-inch Cinema Display requires over 6.75Gbps of bandwidth (because of 8b/10b encoding)”
I’m guessing that the 8b/10b encoding overhead is once again not present in the 10 Gbps per channel Thunderbolt bandwidth figure, just as for PCIe packets. Otherwise Thunderbolt would not be able to fully support the DisplayPort 1.1a spec which calls for 10.8 Gbps when including the 8b/10b padding.
“Apple claims that one of the channels is used for DisplayPort while the other is used for PCIe.”
This still flummoxes me. Does that mean that if you daisy chained 2 4-drive SF-2281 Pegasus R6’s to the Thunderbolt port on the MacBook Pro that you would achieve no better than 8021Mbps combined? That neither device could use the bandwidth of the second Thunderbolt channel even with no DisplayPort device present? Also, although Thunderbolt ports only support DisplayPort 1.1a resolutions, might they still support DP 1.2 features such as MST and daisy chainable displays? Or is the only way to connect multiple displays to one Thunderbolt port by using a DP 1.1a multi-display hub and thereby limiting the resolution of at least one of them to less than 2560x1440?
LedHed - Sunday, July 10, 2011 - link
By the time we have a decent amount of devices starting to use the Thunderbolt interface this will be outdated with the 2nd revision. Once again Apple is raising the price for no gain in anyway.LedHed - Sunday, July 10, 2011 - link
Also calling that huge array box mobile is hilarious in itself.xrror - Sunday, July 10, 2011 - link
So Apple will fix all the nagging issues with Thunderbolt connectivity when... they transition to ARM. Begone evil PC people, I'm sure Apple hates it thoroughly that iMacs and MBP can be "perverted" to x86's domain of Windows.So when MacOS basically is superseded by iOS for their "non-handheld mobile devices" and they finally eliminate iMac and MBP since "people who didn't transition to our new taint-ARM/Apple specific processor" line of devices are obviously just lame, as proven by the poor saps holding on to their PowerPC macs. Yea it's coming full circle.
Ugh... I really hope I'm just being paranoid/joking. But...