Tom's Hardware is reporting test results that show that costly notebook flash drives actually use MORE power than hard drives - shrinking battery life by up to an hour. How could this be?
Testing 4 SSDs against a 7200 RPM 2.5" drive on a Dell Latitude D630 notebook they found
. . . the power savings aren’t there: in fact, battery runtimes actually decrease if you use a flash SSD.
TH stacked the deck using a 7200 RPM drive since the common 5400 RPM drives require less power. 1.8" drives are even more efficient. A smaller form factor doesn't help flash drives since they aren't mechanical.
Marketing from the twilight zone
How could this be? Flash vendors have been touting power savings for over a year and - gulp - they don't exist?
This is as bad a case of high-tech marketing groupthink as I've seen in years.
You can buy better but you can't pay more!
TH went to great lengths to document their results since the outcome was unexpected. Here's some of what they found:
- A Crucial SSD - costing $25/GB - used more power - 1.6 W at idle - than any 2.5" notebook drive requires.
- A Memoright 32 GB drive used a full 2 W at idle
- An Mtron 32 GB flash drive reduced battery life by almost an hour.
- The slowest drive - a year old Sandisk SSD 5000 - almost equaled the Hitachi 7200 RPM Travelstar's energy use. But the SSD offers fewer IOPS than the hard drive!
- They tested against a 200 GB Hitachi Travelstar 7k200, but other 2.5" 7200 RPM drives have similar power envelopes.
What's going on?
TH and I have several theories for the added power use:
- Limited power management TH saw that flash drives have just 2 states: low power and full power. Hard drives have dozens of power saving strategies and features.
- The flash control logic - disk translation layer - requires computing for wear leveling, garbage collection, buffer and cache management, flash mux/demux and the SATA interface - with frequent background operations even when the drive is idle.
- Hard drives are well-optimized and only reach peak power when they have a steady stream of single reads and writes. Elevator algorithms minimize head movement and power with a deep I/O queue.
- It takes 20 volts to write a flash cell - and since you have to write them all to erase a block and then write it with the data - that adds up.
The Storage Bits take
Initially enthusiastic about notebook flash drives (see A flash drive in your future? from 15 months ago), I started getting skeptical after running some numbers (see Power, notebooks and solid state disks).
But not skeptical enough. The power trade-off to get flash performance is grim. Some is tweakable, given enough time and money. Yet the cost/benefit ratio may not give vendors enough of either.
But the real idiots in this are the product marketing people who claimed "longer battery life" to help justify their high prices. Didn't anyone bother to check?
The notebook SSD market is cratering before our eyes
Notebooks SSDs will come nowhere near the 25% market share Toshiba fantasized a few months ago. Server and array SSDs will be popular for the right reasons, and low-end notebooks - Eee-style - that can't afford disks will also use flash to cut cost.
Comments welcome, of course. This won't affect the media player market. They don't need the performance notebooks do.