Ask a Pack Rat
A timely question from a comment on my cheap Momentus XT post and continued in my inbox:
How well does [the Momentus XT] perform in a Mac laptop? What I’ve noticed is substantial slow-down on my older MB Pro when there’s a lot of virtual memory usage (e.g. when running several apps plus Parallels.) For my next MBP (hopefully in the next 2-3 months), I’m considering 2 options:
- Buy [the 500 GB Momentus XT] hybrid drive now, put it into my 1st gen MB Pro, and then move it to a new MB Pro when the boss lets me buy one.
- When I get the new MB Pro, replace its hard drive with a 128 GB SSD, and put the rotating drive into an external (FW800) enclosure. I’ve been tracking my disk utilization, and I figure I can live pretty comfortably within 128gb most of the time, as long as I have storage to move stuff I want to keep around but don’t use every day (e.g. mail archives, my iTunes stuff which I only use on the road, etc)
The interesting thing is these options are just about the same price, not counting the external drive enclosure.
I’ve had the Seagate 500 GB 7200 rpm drive in this (2.33 Core 2 Duo, 2005 vintage) laptop for a couple years now. The fans kick in whenever anything disk-intensive goes on (e.g. mobile account rsync) and that is much more likely to happen when it uses more than 512 MB swap.
The current laptop is maxed out at 3 GB, the new one WILL have a full 8 GB, which should be a big help in reducing/eliminating swapping.
Weighing The Alternatives
It sounds like you’re looking at things the right way: Focused on lower cost and greater benefit without getting taken in by the coolness of SSDs or hybrid drives. And you’re also bringing up a key usability consideration: That external drive enclosure. So let’s weigh the merits.
How Does The Momentus XT Really Perform?
It’s really hard to benchmark a hybrid drive like the Momentus XT. An integrated hybrid drive, the Seagate includes an on-disk controller that attempts to keep its 4 GB of SLC flash memory full of the data you’re likely to ask for. So it’s always trying actively to predict what you’ll need and move that data between disk and flash. This is very different from an SSD, which always uses flash, or a hard disk drive, which mostly relies on the spinning disk for performance.
Most benchmarks are designed to hammer on the underlying storage media, actively bypassing cache. This really causes issues for the Momentus XT in benchmarks like Iometer. The best test of this drive I’ve seen is over at Storage Review, since it includes underwhelming Iometer tests and more-impressive Storagemark results. If you only looked at synthetic tests like Iometer, you’d think the Momentus XT was worthless. But the “workload trace” tests of Storagemark have it outperforming the 10,000 rpm Western Digital VelociRaptor!
The reality is somewhere in the middle: My friends Robin and Howard have both used a Momentus XT in their MacBook Pro, and were happy with its performance. They tell me the Momentus XT makes their computers feel much faster. But another friend, Greg, reports some serious issues with Windows crashing and an odd noise from the drive. Maybe it’s more stable in a Mac than a PC?
In my opinion, the Momentus XT is a nice compromise between “spinning disk” capacity and SSD performance with an emphasis on low cost. If I was going to upgrade my internal hard disk drive today, I’d buy a Momentus XT in a second. After all, I’m using a Mac and the additional cost is negligible. Plus, I tend to carry lots of data around – mainly video files for Final Cut. This last is the reason I haven’t “gone hybrid” myself: I already installed a 640 GB Toshiba drive!
What Are The “All-SSD” Tradeoffs?
The other option is to go all SSD, and this is what most computer vendors (including Apple) have selected for their high-end machines. Flash SSD technology keeps improving, giving better performance and a more-favorable cost/capacity balance. I don’t think 128 GB SSDs are yet available for the same $120 that gets you a Momentus XT, but that would get you the well-regarded 60 GB OCZ Vertex 2. A 128 GB SSD is likely to cost almost $250, changing the economic argument somewhat.
Just about any SSD you pick will absolutely destroy the Momentus XT in both benchmark and real-world performance, but you’d never come close to the hybrid drive’s capacity without doubling the cost of the MacBook with a Kingston V+Series 512 GB device.
This is the SSD curse: Make do with less capacity and more performance or spend an arm and a leg.
Is SSD+HDD An Option?
Then there is the alternate path you suggest: Use both a hard disk drive and an SSD. There are two options here:
- Replace the laptop’s optical drive with a hard disk drive using an adapter like the $99 MCE OptiBay
- Use an external FireWire or USB drive, or repurpose your drive using a case
That second choice might not be an option for everyone. Do you really want to lug around a portable hard drive and cable? Do you want to connect it if you’re on a plane or in a meeting? Then there’s the fact that Macs don’t yet have native USB 3.0 or eSATA, so you’re looking at a maximum of 70 MB/s from a FireWire 800 port.
Either way, you’re talking about manually deciding which data resides on the SSD and which goes on the hard disk drive. Since Mac OS X is not nearly as friendly as Windows about using multiple drives, you’re certain to waste some of that expensive SSD capacity on rarely-used data. That’s fine, it just drives up the cost of the SSD+HDD combination.
One caution regarding SSDs in Apple machines: Mac OS X does not support TRIM, so ordinary SSDs will run into serious performance issues once they start filling up. You need a very aggressive SSD controller to maintain the awesome speed you start with. Something like the Kingston V+100 which uses the latest Toshiba T6UG1XBG controller with the updated firmware Apple uses in the MacBook Air.
I would never want to rely on an external hard disk drive solution, I need too much storage, and I’m too cheap to buy an OptiBay, let alone a decent-sized SSD. If I was in your shoes, I’d have just two options:
- Spend $120 and get the Momentus XT for pretty-good performance and single-disk capacity
- Spend $130 and get the 60 GB OCZ Vertex 2 for awesome performance and hack together some kind of OptiBay alternative
Although the second choice sounds like fun, it’s not a great idea in a laptop. I’m also not too good at manually managing data and would rather have something do it for me. This is why I’m so keen on the Momentus XT!
Given your circumstances, I suggest getting the Momentus XT now for your current laptop and seeing how you like it. If it doesn’t give you the performance you want, you can always go the SSD route with the new MacBook Pro and cry over the you $20 you wasted buying a hybrid rather than a regular 7200 rpm 500 GB drive. For what it’s worth, Apple currently charges $300 extra for a 128 GB SSD.
One word of caution, though: You mention that one of the main causes of performance issues for you is excessive swapping from virtual machines. This is a real red flag performance-wise. The Momentus XT has only 4 GB of flash, and your swapping VMs are going to eat that up, leaving none to accelerate other functions. You might find that the hybrid is even slower than a regular drive in this use case, since the controller would constantly be juggling gigabytes of data between flash and disk. An SSD will do much better with VM swapping, but if you’re not using TRIM you’re going to hit a wall sooner or later. The only real solution for a Mac user is to max out the RAM rather than trying to monkey with faster storage.
A Reader Talks Back
Here’s the opinion of a reader who upgraded his MacBook Pro to use the Momentus XT:
“To follow up on our previous discussion, I decided to buy the hybrid Momentus XT. It’s been in the laptop about 24 hours, and here are first impressions:
- Getting into a pre-unibody MacBook Pro is no picnic! I had to get a Torx #6 screwdriver and used about 6 different little containers to hold all the different kinds/sizes of screw. And getting the top/keyboard assembly off of its clips was a struggle.
- Right away I noticed the machine ran substantially cooler as measured by the fan speed. The previous drive was a Seagate Momentus 500gb/7200 rpm 7200.4, and during disk intensive sessions e.g. TimeMachine backups the fans would crank up to 5000 rpm; they’d be pretty noticeable. With the hybrid, during the same kind of backup activity, the fans have not run faster than 3200 rpm, which is comfortably below ‘notice’ sound levels.
- The machine feels a bit faster, but Parallels definitely felt faster. When I launched Parallels, the machine’s swap usage climbed to 2gb (on top of other stuff I run). Before that would cause a significant hit, but with the hybrid the overall performance, and the performance inside Parallels, felt faster.
So I think this upgrade is a win if you’re considering replacing an existing drive with a 500gb/7200 rpm drive, just on the basis of reduced heat. What remains to be seen, of course, is the reliability of this drive (I’ve had bad luck with Seagate 3.5″ drives.)”