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.

/dev/disk5
#: TYPE NAME SIZE IDENTIFIER
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
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  • deadshort - Sunday, August 07, 2011 - link

    Fantastic: thanks for doing that! Spread the word!

    If the main motherboard and chipset are the same, I guess it stands to reason that a more powerful radio would take a bit more power. ~250 Wh/day, or about 5% of my fairly careless daily consumption, is worth knowing but not worrying about.
    Reply
  • Brian Klug - Sunday, August 07, 2011 - link

    Yeah, I should note that right now idle seems to be around 8-9 watts without much change.

    -Brian
    Reply
  • jalin2 - Monday, August 08, 2011 - link

    I'm in the market to get a new router and was set on getting the E4200. Now I think I'm going to hold off and wait until your router comparison article. Any idea on timeframe when that'll be released? Reply
  • jackwong - Sunday, August 14, 2011 - link

    I would rather go with Apple, the only good Linksys router I have is the WRT54. I also have the e2500 few months ago, I can't believe a 2011 router doesn't has gigabyte ports... and it has connection problem everyday...

    I would rather go with Apple Extreme base station unless the e4200 is way cheaper.
    Reply
  • melgross - Monday, August 08, 2011 - link

    I've had a lot of Linksys routers over the years, stupidly, because every one died. That includes some commercial models. I will NEVER use another Linksys product again.

    I've got one Extreme, and two Expresses, and have never had a problem with them. As the review says, they just work.

    I've got an old house, built in 1925. Most interior walls are brick. All the walls and ceilings have .75" wood over the brick, with gal steel mesh over that, with .75" mortar, and a .25" layer of plaster over that. The damn thing is as close to a Faraday cage as anyone will ever live in. I've removed some of that when re-doing the kitchen and downstairs bathroom as well as the two bathrooms upstairs by having everything stripped to the beams and replaced with double .5" Sheetrock, but still...
    Reply
  • Guspaz - Monday, August 08, 2011 - link

    Perhaps some mention should be made of the fact that Apple advertises the drive in the Time Capsule as a "server-grade hard drive".

    You do mention that it's very much a consumer disk (in fact, the most "consumer" you can get since it's not even a black or RAID edition), but Apple is really billing the thing as server-grade, which is false advertising.
    Reply
  • jwoelich - Monday, August 08, 2011 - link

    "Fortunately, a source inside Western Digital was willing to explain matters; "If you enter in the drive number on NewEgg you're going to see it come up as a desktop drive. That platform is actually built on a lot of other products for a lot of different OEMs. And the specs could change depending on whatever program we're building for. Needless to say Apple has very stringent requirements that are very specific to them and very unique to them, and that drive has actually been developed and is unique for that Apple product. That unique Apple logo, and what we call 'to the right of the dash,' if you will, indicate that this drive is for a very particular partner to us and this drive is dedicated to that particular audience. You could not buy this same drive at NewEgg or Amazon."

    When we asked whether the variation of the WD20EARS drive is rated for a 1-million-hour MTBF, our source confirmed that it was: "We don't spec our desktop drives with MTBF because our customers don't purchase in that manner, but this particular drive for this particular OEM with these unique requirements does meet those specifications."

    Western Digital says otherwise.
    Reply
  • repoman27 - Monday, August 08, 2011 - link

    lowlymarine did mention it in a comment two days ago, to which I pointed out that for price per GB and performance per watt the Caviar Green is tough to beat, and therefore perfect for servers. Just considering how many Google uses, I would be surprised if there is another line of drives more deployed in servers at the moment than Caviar Green.

    Not all "servers" are designed for crazy amounts of IOPS, massive queue depths, or incredibly high availability. For backup or redundancy, which is what the Time Capsule is marketed for, you want big, cheap and low-power.

    No offense, jwoelich, but although the quote may be legitimate, I have a seriously hard time buying that line of utter crap. We're pretty much down to a three horse race in the storage arena, and just like Intel or AMD might bin things differently or cater to large OEMs in various ways, they basically just pump out a small range of identical products by the millions. There are no "magical drives" that are perfect for servers but not sold by Newegg. The way I read it, Apple had a very stringent range of specifications, to which a bog standard Caviar Green drive happens to adhere perfectly (i.e. low price per GB and low power requirements.)
    Reply
  • jwoelich - Tuesday, August 09, 2011 - link

    I don't see where anyone stated anything being 'magical', just that if you were to go onto Newegg, you couldn't just order one of these specific drives. Now, does that mean that there is more to it than Western Digital simply taking any WD Green drive, testing it to conform with the criteria set forth by Apple, then throw on a new sticker? Or did WD design/modify a product specifically to meet that criteria? More likely, WD crafted a Frankendrive using the criteria Apple set forth, and used the bare minimum of higher quality components that would more likely ensure that criteria was met, which was probably nothing more than power consumption, size, speed and a greater MTBF. Reply
  • LoneWolf15 - Monday, August 08, 2011 - link

    "Some more searching revealed the solution—pin 20 (wireless disable) needs to be taped over to signal the card that the wireless disable switch (which doesn’t exist, since this is the WAN port) is in the on position. A quick surgical application of tape, and the card worked perfectly—take that, Lenovo security. As an aside, what a completely pointless and trivial barrier this is—the Mini PCIe standard (and moreover WiFi notebook cards themselves with U.FL connectors) are designed to be completely and absolutely interchangeable. The notion that this provides any added security (when the adjacent slot is completely unguarded) or—even more absurd, convenience—is nothing short of a surrealist notion."

    Lenovo isn't the only one. HP also does the exact same thing; they whitelist cards in the BIOS, so that only their branded version of Intel's (or Broadcom's) wireless cards work.

    I don't think security has anything to do with it. I think two factors are involved --1) that they don't want to support any other wireless cards than their own, and 2) that they want you to buy from them, establishing vendor lock-in.
    Reply

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