Disk Performance

The next question on my mind was disk performance. I don’t own a Time Capsule for backing up my singular Mac; instead I use a hard drive dock attached to the Airport Extreme over USB 2.0 for that purpose. So the question now becomes, is it dramatically faster to use the Time Capsule’s internal disk over SATA II instead of a USB 2.0 attached dock? The question is almost rhetorical (of course SATA II is going to beat USB 2.0, right?), but nevertheless we want numbers.

When a disk is attached with USB to the Time Capsule or Airport Extreme, you have the option of sharing the disk like an ordinary AFS or even SMB share with or without a password. The Airport Extreme or Time Capsule pops up under devices in finder, and then you can mount specific shares which appear just like a normal volume to OS X. Rather than time the creation of an entire fresh Time Machine backup on each configuration, I settled on measuring performance across the network to the drive using QuickBench while connected over GigE.

Before we go into the performance numbers, let’s talk about changing out drives in the Time Capsule. The nice part about the Airport Utility is that there’s a one-click erase button for automatically partitioning any drive properly for the Time Capsule. There are even options for making that wipe take place with multiple passes in case you’re trying to delete some really shady, erm, scientific research.

Anyhow, clicking erase from the airport utility makes the drive usable without the need for any preformatting. It’s almost as if Apple expects people to try to upgrade the disk on their own in the future or to make it easy to service. Doing so and then taking the drive out for inspection reveals three partitions. You can see these three partitions by running diskutil list on the drive.

0: GUID_partition_scheme *240.1GB disk5
1: Apple_HFS APconfig 1.1GB disk5s1
2: Apple_HFS APswap 1.1GB disk5s2
3: Apple_HFS Untitled 1 237.9GB disk5s3

So no matter how you slice it, you lose 2.2GB to overhead just from the Time Capsule partitioning things how it wants. I couldn’t find anything inside APswap, at least after a fresh format. Inside APconfig is a file named AFP.reconnect_keys which contains a mysterious unintelligible string, perhaps a hash of some kind or a token used to authenticate clients. Regardless, it’s apparent that the architecture for Time Machine on a Time Capsule differs from the external disk method when a drive is attached over USB. I learned on my own that these backups aren’t easily portable between the two, though you can actually migrate backups off of the Time Capsule to an attached disk by clicking Archive.

When using the disk attached using USB however, you have to preformat the drive as HFS+ yourself, but in that case one large partition suffices. Then you back up to .sparsebundles inside that, and essentially Time Machine treats the thing like a network attached drive.

So on to the performance testing. In true AnandTech fashion, the disk I chose to use for testing was a Vertex 3 MAX IOPS 240GB SSD, just to eliminate the disk as being a potential bottleneck in the performance benchmarking. To start, I took a baseline test with my rather generic Rosewill USB 2.0 dock attached directly to the MBP. Next, that same volume when connected across the network to the Airport Extreme using USB 2.0, then the Time Capsule using USB 2.0, and finally installed inside the Time Capsule using SATA II (3.0Gbps). I present to you the (probably) first Time Capsule with an SSD inside.

For good measure, I also tested the Time Capsule with the shipping 2TB WD Green, and one of my own personal 3TB WD Greens inside, just to see how platter drives fare. I also threw in one test where I connected over WLAN instead of gigabit ethernet directly to the devices.

First up is sequential read speeds, which aren’t critically important for backing things up (since you’re probably more concerned with write performance) but hugely important for restoring and verifying or indexing backups. Connected directly to the devices, we can essentially max out gigabit ethernet with 80+MB/s transfers, or just shy of 700 Mbps. Some individual tests are even at 100MB/s (800 Mbps), but these are the averages of those 20-100MB size tests.

Sequential Read Speeds (20-100MB Transfer Average)

SATA II here gives a huge advantage over USB 2.0 and comes close to hitting the limits of gigabit ethernet. Oddly enough, USB 2.0 performance isn’t even limited by the dock, but rather the controller. Connected directly to the notebook, performance is almost 10MB/s faster.

Sequential Write Speeds (20-100MB Transfer Average)

Reads show a similar, if interesting, story. SATA II again proves noticeably faster than the USB 2.0 route, but performance seems capped to around 40MB/s. Obviously the Vertex 3 can write way faster than this, but the controller seems to be strained to the limit when making writes. This is a bit frustrating considering mostly what the device is going to be doing is writing stuff to disk every couple of hours.

As Anand will tell you, no sequential write is ever really truly sequential, so small block performance is also important. I selected the 4 KB block test and analyzed results, which show that for writes we’re pretty much limited to the same 1.0MB/s even on a stupidly fast SSD both over SATA and USB 2.0, again the controller or network overhead with so many small transfers seems the limit.

Sequential Write Speeds (4 KB Transfer Average)

On reads, the same story applies, with everything stuck around 8MB/s over gigabit or the dock. WLAN performance suffers considerably.

Sequential Read Speeds (4 KB Transfer Average)

If you’re going to be doing lots of backing up and care about speed (or don’t mind the extra price), the Time Capsule’s SATA II interface makes it a considerably faster experience compared to the cheaper USB 2.0 dock solution. It ends up being twice as fast at writing and over three times as fast at reading to use the Time Capsule over the Airport Extreme. Of course if you’re going to be using WiFi to back things up, all bets are really off and the performance gains of using the Time Capsule over the Airport Extreme largely erode away.

WiFi Throughput and Range - Improved Airport Utility and Networking Functions


View All Comments

  • Amia - Wednesday, August 17, 2011 - link

    Under 5g my Mac air is getting 270mbps but my another laptop which used to get 300mbps using my previous router can only have 150mbps. Maybe just like Mac air apple doesn't want you to use dual band (40mhz) under 2.4ghz Reply
  • MobiusStrip - Wednesday, August 17, 2011 - link

    It would be nice to see a comparison of Airport with other brands of wireless routers. Reply
  • Flachr - Friday, August 19, 2011 - link

    I noticed that the 5g Extreme's country field in the airport utiliy is limited to very few countries while all my previous TC's had a long list of countries to choose from.
    Is Apple now tailoring devices to regions? Is there a way to get the longer list of countries back to select from?
  • IdBuRnS - Monday, August 22, 2011 - link

    I have been using my Airport Extreme (MD031LL/A) for about a week and a half now and I'm loving it. It replaced an old Netgear G router so it's like night and day between the two when it comes to streaming wirelessly.

    Since I have FiOS I only use it as an AP (FiOS router is in my wiring closet in my garage which puts it out of range for all my devices) but so far I couldn't be happier.
  • Jack iCaseReview - Friday, August 26, 2011 - link

    I don't think the AirportExtreme will ever be a good solution for massive network backups. For small backups it great, but anything too big, and it somewhat slow....

    editor - www.iCaseReview.com
  • MarsMSJ - Sunday, September 04, 2011 - link

    I had bought an E4200 to replace a WRT310N that started acting up (going unresponsive.) I had issues where I would get abysmal download speeds on wired. I moved my cable modem to as few splits as possible and that resolved most of the issue (though I argue that my speeds were fast for a year until 2-3 weeks ago and the split had nothing to do with it. Now I get 8-12 where as I had 12-15 for though it's better then the .5 I was getting.)

    Anyway I noticed right away that when connecting the E4200 my speeds are cut by a 1/2 in comparison to connecting directly to the modem. I upgraded to the latest firmware which not only did not fixed the issue, but broke other features of this router (media server does not work among other things.) Cisco is testing new firmware that won't be available until the end of September if everything goes well.

    I found this out because I got an the new Airport Extreme Gen 5 for my side of the house recently. I got curious and switched out the new AE and saw that my speeds were as fast as connected directly to the modem. I spent my Saturday night testing these both by themselves and my notebook and confirmed the E4200 is cutting internet speeds in half. When I hooked everything up the speeds were similar to when I was the only device connected to it.

    Right now I have the AE Gen 5 connected to the modem on the other side of the house while the old WRT310 is on my side with my devices wired in (no wireless on my side for the moment.) Wired into the WRT310 which is wired to the AE Gen 5 (we have a 100 foot cable that runs outside along the roof) and using speedtest.net (used them and the same server for all testing) I get 7-9 Mbps compared to the 2-4 on the E4200.

    Something is definitely wrong and luckily I got the E4200 at Best Buy on sale (130USD though it's back up to 180) and they have a 45 day return policy for Reward Zone Silver members (Dad bought a mac book pro from them thus spent enough to qualify.) I will be returning it and maybe getting another AE Gen 5 or just waiting it out to see if the new firmware fixes the E4200 download/upload speed issue. (I can live without wireless in my room for month.) If you're debating, now is not the time to buy an E4200.
  • milan03 - Saturday, September 17, 2011 - link

    You can totally share a printer using Airport Express. I've been doing it since the 4th Gen. Reply
  • tekenaar - Monday, October 24, 2011 - link

    . . . is: "At this point it isn’t really looking like there’s much different, but exterior appearances can be deceptive."

    . . . S/B: "At this point it isn’t really looking like there’s much difference, but exterior appearances can be deceptive." ?!
  • silvalli - Monday, October 24, 2011 - link

    Can't find discussion of this anywhere. Reply
  • spaztec - Friday, December 23, 2011 - link

    Noticing a fizzing sound coming from my unit during wireless data transfer - any techs here with insight as to which exact component is causing it? I'd check myself, but voiding the warranty for curiosity's sake sounds like a bad idea. Reply

Log in

Don't have an account? Sign up now