A hybrid of SSD and hard drive that gives you the best of both worlds. Seagate’s new Momentus XT on my 17″ unibody MacBook does it. Almost.
Specs
Take a standard issue 7200 rpm, 500 GB notebook SATA drive. Add 4 GB of fast and reliable single-level cell (SLC) flash. Make it look like a standard drive to the OS by keeping all the magic internal.
Give it smarts to learn about high-frequency small-block transfers. Put those blocks in the flash and voilà: super-fast small block access; leaving big sequential I/Os to the disk.
For a lot less money!
Theory
Disk drives offer cheap capacity and good large read/write (R/W) bandwidth. The R/W bandwidth improves over time as drive capacities grow due to higher bit density.
Flash SSDs offer sub-millisecond access times at a high price: $2-$3/GB. SSD access times are about 150x faster than a notebook hard drive, while R/W bandwidth is only about 2x faster.
Maximum bang for the buck? SSD to store many small files - like DLLs in Windows - to minimize accesses, and let the disk handle the large R/W traffic. Why pay 40x for a 2x performance boost?
Flash capacity? 4 GB can store 4 million 1k files. That saves a lot of access time.
Test
An early 2009 17″ unibody MacBook Pro with 4 GB RAM and 2.66 GHz Core Duo 2. Swapped the current 7200 rpm, 500 GB Hitachi for a 7200 rpm, 500 GB Momentus XT with 4 GB SLC flash.
For the first test I formatted it with HFS+ using the Mac’s Disk Utility. Then I used the excellent Carbon Copy Cloner to clone the system disk to the XT.
Results
Boot performance sucked compared to the old drive’s ~45 second boot:
- First boot took 2 minutes 4 seconds
- Second took 1 minute 19 seconds
- Third took 1 minute 6 seconds
After consulting with Seagate I did a clean install of OS X. Reformatted the XT, installed Mac OS 10.6 Snow Leopard, migrated accounts and data. Took 3 hours, but the process worked perfectly.
New boot times went to ~45 seconds again. Not what I had hoped - the SSD on my MacBook Air booted in 15-20 seconds - but competitive. Other testers have had better results so Seagate is sending me another drive. I’ll update the results later this week.
Application results were much more impressive. Because the drive learns, the first time you bring up an app it happens at disk speed. But the 2nd time!
Mail startup went from 5 seconds to 1.5. Microsoft Word startup went from about 12 seconds to less than 3. See for yourself in this 15 second clip:
And the bigger the app, the bigger the potential speed up. Look at this 1 minute clip of the 1st and
From 45 seconds to 10 17? Way faster than my Mac Pro’s 10k system disk.
Note that rarely opened apps won’t do as well as the algorithm favors apps that get used more often. Pure SSDs don’t have that variability.
Pricing
Announcement pricing:
- 500 GB/$156
- 320 GB/$122
- 250 GB/$113
These prices are about double the street prices for the non-hybrid drives. Once Seagate gets some competition they should drop.
The Storage Bits take
Looks like a home run for Seagate. The architecture is clean, the performance advantages are real, and pricing is not too bad - especially compared to SSDs.
SSD adoption has stalled because flash prices have firmed up. Few are willing to pay $200-$300 for a smallish SSD in a $700 notebook. But $100? OK.
Seagate could use cheaper MLC flash in 8-16 GB caches without wearing it out. There is every reason to put this in 3.5″ drives as well. After all, if the flash does fail all your data is on the hard drive - no loss there.
By blurring the performance difference between disk and SSD, these drives will ensure that hard drives dominate for at least another decade. And they’ll put pressure on SSD prices.
But don’t count on these showing up in RAID arrays soon. Arrays already have a lot of moving parts and hybrid drives add some subtle wrinkles.
Comments welcome, of course. No money changed hands, but I must say that I’ll be reluctant to return the review unit. Update: As a number of commenters pointed out - thanks! - I screwed up: the original video showed a reboot from system cache. When I got the time I reshot the FCP startup after a reboot. It was still 40% of a regular drive and still much faster than a 10k drive on my Mac Pro. Sorry about that! End update.
