Promise Pegasus R6 & Mac Thunderbolt Review
by Anand Lal Shimpi on July 8, 2011 2:01 AM ESTDisplayPort Passthrough
The Pegasus has two Thunderbolt ports. You can use the second port to daisy chain up to six Pegasus devices together, for up to 36 drives. With a single Pegasus in its default configuration able to hit over 5Gbps, you'd definitely run into bandwidth limitations with six of these things. But you could get by with two and not be limited by Thunderbolt.
There's another role that second Thunderbolt port can play: as a DisplayPort output. Remember both PCIe and DisplayPort are carried on a single Thunderbolt cable, the latter occupying half of the 40Gbps of total bandwidth available.
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.
I connected a 27-inch Cinema Display through the Pegasus without any problems. The Pegasus does have to be on for you to get video however, so if you ever have to shut down the Pegasus you do lose video to the Cinema Display.
Audio still works, so you'll see the Cinema Display as an audio device on your Mac:
The experience is pretty seamless overall.
I ran a quick test to see if I lost any bandwidth to the Pegasus with the 27-inch Cinema Display in the chain. I measured a slight performance drop (< 3%) in the best case scenario of four SF-2281 SSDs in a RAID-0 array on the Pegasus, but nothing substantial at all. Note that simply displaying an image at 60Hz on the 27-inch Cinema Display requires over 6.75Gbps of bandwidth (because of 8b/10b encoding), so a full Thunderbolt channel is necessary for DisplayPort (although admittedly it only needs to be unidirectional bandwidth).
| Thunderbolt PCIe + DP Bandwidth Test | ||||
| 2MB Sequential Write, QD16 | No DisplayPort Passthrough | 27-inch Cinema Display Connected | ||
| Promise Pegasus R6 (4 x SF-2281 SSDs, RAID-0) | 1002.7 MB/s | 988.2 MB/s | ||
Facebook
Twitter
RSS
88 Comments
View All Comments
enthios - Thursday, July 28, 2011 - link
"Ironically isolated from the world around them?" How about wifi and iCloud? With limited storage capacity, there's no need for anything more. iOS devices are simply thin clients - and they work wonderfully as such.NirXY - Friday, July 8, 2011 - link
Which is 0$Exelius - Friday, July 8, 2011 - link
Yes, but in this instance, it's not just a dumb wire; there is an IC at each end of the cable. So theoretically, if Intel comes up with an upgraded Light Peak spec, there may well be cables that are capable of faster speeds. I also imagine longer cables become more difficult, and may in fact require fiber optic transceivers built into the cable. This cable also likely costs significantly more to manufacture than a crimped cable, since there's a tiny IC and micro soldering that needs to be done on each cable.But yes, in one sense you are right that in a digital bus, higher quality cables do not provide better performance (though I have run into very low-quality HDMI cables that work fine at 720p but refuse to carry a 1080p signal.)
repoman27 - Sunday, July 10, 2011 - link
At the moment, i’m not sure the Thunderbolt host controller has any real legs on the cable. That host controller is already pumping data to each port at the same speeds as the DMI link between the CPU and PCH. Everything in the chain that is connected to it needs to get faster for Thunderbolt to get faster, i.e. PCIe 3.0, DMI 3.0, DP 1.2.Also, I’m pretty sure it’s not those little ICs that are making Apple’s Thunderbolt cables cost $49. Like many retailers, Apple knows that cables and accessories (and RAM upgrades) are a great place to stretch profit margins. A quick search of the Apple store for cables and adapters will turn up dozens of genuine Apple offerings ranging in price from $19 on up to $99. So, taken in context, the Thunderbolt cable is actually a mid-priced cable from Apple, not an expensive one. It also means that cheap unbranded alternatives could quite realistically be sold for around $15, ICs and all.
Regarding your HDMI cable experience, Category 1 or “Standard” HDMI cables are only rated for 1080i60, whereas Category 2 or “High Speed” cables will do 1080p60, 4K, 3D, Deep Color, etc. Older cables weren’t marked as such, and thus YMMV.
snakeInTheGrass - Friday, July 15, 2011 - link
Yeah, the SCSI cables were $75+ easily, you needed terminators, and do you remember the fine SCSI1/2/3 connector differences so you needed adapters or cables with different ends depending on the devices. I still have probably what WAS $500 of cables in my closed.Inflation adjusted, these $50 cables are about the equivalent of $15 cables back in those days, so frankly they don't sound too bad, especially considering the fact that it's industry leading performance right now.
As for comparing to Monster cables, these Thunderbolt cables have controllers built into them and presumably do have to meet tighter tolerances than USB, particularly as they carry 2 x 10Gbps data streams. But you're right that Monster cables are a rip off.
flowynn - Friday, July 8, 2011 - link
I remember those days well. My need for speed SCSI habit was insanely expensive.MonkeyPaw - Friday, July 8, 2011 - link
It reminds me of FB-DIMMs, an expensive solution that uses additional energy, and the components cost more than devices it replaces. Controllers in the cables AND on the motherboard and peripherals? Maybe the optical solution will make more sense.CrimsonFury - Monday, July 11, 2011 - link
I thought the initial copper cables didn't need any controllers in them? The impression I got from earlier articles was that Intel said their Thunderbolt implementation could scale to optical in future for greater speeds by releasing optical cables with a copper to optical controller in each end of the cable once controller costs had come down from mass production.MobiusStrip - Tuesday, July 12, 2011 - link
No, they need optical in the ports and wires.By reneging on the light in "Light Peak", Intel effectively killed it. Who knows why they're playing dumb in pretending that they're going to get the industry to adopt Thunderbolt and then turn around and adopt an optical solution right afterward. Just idiotic.
André - Friday, July 8, 2011 - link
I find it especially funny considering that all current Thunderbolt solutions (A/V equipment or storage enclosures) are all in excess of $999 to begin with.