That’s a screenshot from my favorite free tool for testing hard disk performance–HD Tune (there’s a pro version you can buy, too). That’s from my Seagate Barracuda 7200 RPM 1.5 TB SATA drive backup drive.
The Blue Line–Transfer Rate
First, the blue line is the transfer rate. That’s the speed which the hard disk sends data to the computer when a big file is lined up nicely–defragmented, in other words. Notice that the line starts high (at 126 MB/sec) and drops (to about 57 MB/sec). That’s because the test moves from the outside of the drive to the inside. Disk drives are round, like a record, and so the outside spins faster (in inches/sec) from the inside.
Windows starts storing data on the outside of your disk, and works its way towards the center. That way, your files will be as fast as possible. The fact that the performance drops by 65% from the outside to the inside of the disk helps illustrate that disk performance is WAY better for files stored on the outside of the disk. It also shows one big reason why, as your disk fills up, it also slows down.
The Yellow Dots–Access Time
The yellow dots show random access time. That’s the time it takes for the disk to jump from one part of the drive to the next. In other words, that’s how long it takes to jump from the end of one file to the beginning of the next, or to jump between two segments of a fragmented file. The average access time for this disk is 13.5 ms–but lower would be better.
USB Flash Drive Performance
The previous graph shows typical performance from a hard disk, but USB flash drives behave very differently. They don’t have spinning platters–data is read by sending electrical signals. If you think they’ll be faster, you’re right. If you think they’ll be slower, you’re right.
As you can see, the transfer rate is WAY slower. My Seagate had an average transfer rate of 100 MB/sec, but my USB flash drive was at 16 MB/sec–about 6X slower. The access time is 0.8 ms, though–about 17X faster. So, USB flash drives are faster at random access and slower at sequential reads.
ReadyBoost uses this to improve the performance of Windows by caching files from the hard disk to a flash drive. If it would be faster to read it from the flash drive (like, if it’s a small segment of data that would need to be randomly accessed), it reads it from the flash drive. Otherwise, it takes advantage of the hard disks high sequential read performance.
Many new mobile computers ship with flash drives instead of conventional disk drives. In some ways, performance is better, and in other ways, performance is worse. The transfer rates of flash drives will increase over time, however, and Windows 7 includes some major improvements that speed up flash drives.
How to Get the Best Performance
I do a great deal of photo and video editing with my Canon EOS 5D Mark II–that’s 21 megapixel pictures and 1080P video–and a really fast disk makes things much more efficient. When I bought a new computer, I set it up with a very fast disk subsystem. Not the fastest in the world, mind, you, but a good bang for the buck. I chose two EXPENSIVE 15,000 RPM disks and put them in a RAID 0 array, which reads and writes to both disks at the same time. Here’s the performance I got:
Overall, that’s about twice as fast as my 1.5 TB drive (though I might have expected better…)
On Laptop Performance
So far, I’ve been discussing the disk performance of my desktop computer (a Dell Precision T3400). The main reason I bought a desktop was to get better disk performance–laptops tend to be really bad, owing to the use of small disks. Remember my lecture about how disks perform best at the outside edge of the platter? Well, smaller disks have smaller outside edges, so performance drops. Laptop disks also tend to be optimized to reduce power usage, so they spin at a slower RPM. Here’s the disk that shipped with my Dell D820:
Abysmal, right? The average transfer rate is 3X slower than the cheap Seagate drive I began this discussion with. All hope is not lost, however. It’s not too hard to upgrade a laptop hard disk–just backup to an external disk, swap drives, and then do restore to the new disk. I upgraded to a newer, faster, 500GB drive and got this performance:
The new disk doubled the average transfer rate (though the access time actually dropped a bit). It sped up the computer noticeably. So, if our laptop seems slow, upgrading the disk might be the right choice.
Got a fast or slow disk? Need some advice about hard disk performance? Tell me about it in the comments.