A Tale Of Two Thunderbolt Storage Devices: Seagate's GoFlex Desk and Western Digital's Thunderbolt Duo
by Brian Dipert on May 13, 2012 7:52 PM EST- Posted in
- Thunderbolt
- Seagate
- WD
- Western Digital
My initial assumption had been that WD put a hardware RAID controller between the Thunderbolt interface and the two SATA HDDs, akin to what Promise had done with the Pegasus, and as has also been the case with any number of other dual-drive enclosures I've tested and otherwise used over the years. The fact that the Thunderbolt Duo didn't have configuration switches (an O/S-agnostic and otherwise convenient means of setting the RAID mode in hardware versus via a software utility) gave me pause, but not all hardware RAID controller-based enclosures I've used have had them.
However, after powering up the Thunderbolt Duo for the first time, I happened to fire up Mac OS X's built-in Disk Utility and received clear indication that the enclosure was (as with the LaCie Little Big Disk) instead leveraging Mac OS X's native software RAID facilities:
As previously mentioned, I promised my WD PR contact that I wouldn't take the enclosure apart. But I'm guessing that, akin to the LaCie Thunderbolt eSATA Hub that Anand saw at CES 2012, WD has built into the Thunderbolt Duo a Thunderbolt to dual SATA controller. Such a feature allows the system-side Thunderbolt controller to "see" each Thunderbolt Duo as a single bus peripheral, thereby enabling WD to accurately claim that you can daisy-chain numerous drives to each other and the system before you violate Apple's six-max specifications.
WD includes the installer for WD Drive Utilities, a status-and-configuration program, right on the Thunderbolt Duo, although I found (and downloaded, installed and used instead) an updated version of the utilities at the company's support website:
However, I found myself using Mac OS X's Disk Utility in this study instead, for several reasons (and with WD's official sanction, as it turns out). For one thing, Disk Utility offers the auto-rebuild-on-error option for RAID 1 (mirrored), a setting that isn't exposed in the WD program. Also left unexposed in the WD utility are the five block-size options (16KB, 32KB, 64KB, 128KB and 256KB) that Disk Utility supports for both RAID 0 and RAID 1; I'm assuming (but don't know for sure) that WD's program uses Mac OS X's 32KB default block size setting.
WD's program offers the "JBOD" ability to use the two HDDs as discrete drives, even optionally putting HFS+ on one and exFAT on the other, which is convenient for dual-O/S-booting purposes. However, surprisingly, the WD utility does not expose Disk Utility's 'Concatenate' option, which combines the two drives in a non-striped fashion. Although SPAN (i.e. BIG) is not an official RAID mode, it's commonly supported by RAID utilities. And curiously, although the WD utility doesn't support configuring the drives in SPAN mode, it correctly identifies a two-drive array that's already been concatenated via Disk Utility:
One historical reason (of many) for going with hardware RAID is that (versus software RAID) it didn't excessively burden the CPU, with both resultant system battery life and performance impacts. Thankfully, if my experiments are indicative of a broader conclusion, those days are over. Note that the kernel_task process reports using only around 6% of one core of the CPU during heavy use of the Thunderbolt Duo in RAID 0 mode, and that the system reports four cores (thanks to HyperThreading virtualization):
Given that kernel_task typically consumes 3-4% of a CPU core under normal operating conditions, an extra few-percent load for heavily utilized software RAID is, in my opinion, quite acceptable.
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name99 - Monday, May 14, 2012 - link
"Given that the PCI Express channel of the Thunderbolt interface delivers 10 Gbps of peak bandwidth in either direction, I next decided to see what would happen if I tethered the Seagate and WD drives together."You can do even better than this. You should have been able, in Disk Utility, to create a striped drive consisting of the two WD drives and the Seagate drive. This would be gated by the speed of the slowest drive, so should give you around 360MB/s read and write speeds.
Disk Utility is not perfect, and god knows I've sent Apple long lists of ways it can be improved; but it is pretty awesome for basic things like creating either striped arrays or large concatenated arrays.
bdipert - Monday, May 14, 2012 - link
Dear name99, that's a great idea. I'm traveling at the moment but will give it a shot when I get back in front of the Mac mini. I agree with you that it conceptually should work, and will be performance-gated by the drives in the Thunderbolt Duo.Torrijos - Monday, May 14, 2012 - link
You talked a bit about the impact of running a soft-RAID device being negligible, it would be nice to know the impact on the OS when pushing those mass storage devices to the limit.I've bought an USB3 extension card for my mac and while transfer speed are great, OS responsiveness takes a hit every time a big transfer occurs (TM backups are a pain).
A formal test of the impact of USB 3, ThunderBolt would be nice.
repoman27 - Monday, May 14, 2012 - link
Have you watched Activity Monitor during a TM backup to see what's being stressed? I usually associate the performance drop during TM backups with the crazy amount of small random reads that need to be performed on the system volume while you're still trying to use it.Draconian - Monday, May 14, 2012 - link
So basically, if you're really concerned about performance, an SSD using an old 3 Gbps connection will read and write twice as fast as a HDD using a Thunderbolt connection?I would be interested in knowing what the results would be with a HDD using an eSATA connection. And of course USB 3.0.
jabber - Monday, May 14, 2012 - link
......companies selling 7N Thunderbolt cables that cost them $3 to make but selling them to audiophiles for $3000 a go.Glindon - Monday, May 14, 2012 - link
Each connector of the thunderbolt cable has a small chip, which is why the cable costs so much. It's not just a $50 cable. iFixit has done a tear down of the cable if you want to check it out.repoman27 - Monday, May 14, 2012 - link
There are quite a few factors which make Thunderbolt cables expensive, being an active design is just one of them. If you ignore the bit about Thunderbolt being intended for iOS devices, the following blog post reveals quite a few details:http://www.patentlyapple.com/patently-apple/2012/0...
I think the snake oil salesmen that prey on the audiophiles will avoid Thunderbolt for some time, specifically because it is an expensive to manufacture, high bandwidth cable that can't be made for $3. A 2.0 m copper pipe that can carry 20 Gbps, full-duplex, plus bus power and out-of-band signaling just doesn't exist yet in the sub $20 realm.
quiksilvr - Monday, May 14, 2012 - link
You pay an arm and a fucking leg for these things and they don't even have the god damn decency to give you the wire?CalaverasGrande - Monday, May 14, 2012 - link
Just like on the MAc centric forums, people can not look past their narrow usage scenario to accommodate other perspectives.I work at a TV station, but have a background in audio production. In most prosumer studios, and quite a few mid level studios, firewire is the connection of choice for audio interface (soundcard). The high end audio interfaces have until recently all been either a PCIe card or Firewire. Add to the pile firewire based DSP such as the UAD-2 and firewire disk arrays used to insure fault tolerant and fast nearline storage.
In video production we really don't use 1394 anymore. But there are still some old boxes in use that have the mini connector. Often they get pressed into use as a transcoder or layback machine for formats we dont use natively anymore. We are all on Sony XDcam disk, which I would love to see as a consumer format!
I personally can't wait to see wider adoption of thunderbolt. I plan on upgrading to a T-bolt equipped mac after the next refresh of the MBP line.