Performance Showdown - SSDs vs. HDDs

Very interesting data posted on slashdot:

"Computerworld compared four disks, two popular solid state drives and two Seagate mechanical drives, for read/write performance, bootup speed, CPU utilization and other metrics. The question asked by the reviewer is whether it's worth spending an additional $550 for a SSD in your PC/laptop or to plunk down the extra $1,300 for an SSD-equipped MacBook Air? The answer is a resounding No.

Surprising performance results

“I used HD Tach to test the drives' performance -- and got some interesting results. It was the mechanical Momentus drive (non-SSD) that scored the highest burst speed at 214.3MB/sec. The Crucial SSD came in second at 137.3MB/sec., but the desktop Barracuda (non-SSD) and its 135MB/sec. clung to its heels. Advanced Media's Ridata drive trailed the pack at a leisurely 71.2MB/sec. While the two mechanical drives and the Ridata SSD posted average reads in the 54MB-to-55MB/sec. range, Crucial forged ahead at 120.7MB/sec.

SSDs are highly praised for their boot speed, so I would have been remiss had I relied solely on a standardized test. The results were a bit surprising. Crucial's SSD and the two Seagate devices all required 39 to 40 seconds to cold boot to the desktop. (There are a few minutes of behind-the-scenes activity during a Vista boot, but I determined that the boot was complete once the Windows sidebar appeared.) Ridata did best of them all, with a boot time of 32.1 seconds, although that's hardly the blazing speed you might expect from an electronic versus a mechanical device.”

Moving data

“Finally, because these SSDs have a comparatively small capacity, it's most likely that you will be transferring data from your laptop after a day's work. So I took 4,666 files and folders (a total of 8.05GB) and copied them to the drives and then copied them from those drives. I used the same secondary drive as source and destination in all cases.

Neither of the SSDs fared very well when having data copied to them. Crucial needed 243 seconds and Ridata took 264.5 seconds. That's over four minutes. The Momentus and Barracuda hard drives shaved nearly a full minute from those times at 185 seconds. In the other direction, copying the data from the drives, Crucial sprinted ahead at 130.7 seconds, but the mechanical Momentus drive wasn't far behind at 144.7 seconds. Ridata and the Barracuda were third and fourth at 156.8 and 166 seconds, respectively.”


More details here.

Disk storage - where are we headed?

Some insightful articles and some of my own thoughts on the trends in data storage:

THE BACKGROUND:
Disk capacities are going up and costs are going down, however the effective transfer bandwidth (ETB) per byte of capacity has come down tremendously. Despite capacities and transfer rates increasing by factors or 10,000 and 100 respectively, typical drive ETB has actually decreased by a factor of 100. As Jim Gray said "Disks have become tapes." (Link to source).

Consider, for example, a 10 TB database. Ten years ago, this database would have occupied two thousand 5 GB drives - a common size at the time. With a 3 MB/second transfer rate, the aggregate bandwidth of these 2,000 drives would have been 6 GB/second, enabling the entire database to be scanned in about 30 minutes. Today, only about 20 higher-capacity drives would be needed to hold this same database. Those 20 drives would have an aggregate bandwidth of 1.2 GB/second, increasing the time required to scan the entire database to 150 minutes - an increase of two hours.

DISKS ARE BECOMING A SEQUENTIAL ACCESS DEVICE RATHER THAN A RANDOM ACCESS DEVICE
Jim Gray points out - We have to convert from random disk access to sequential access patterns. Disks will give you 200 accesses per second, so if you read a few kilobytes in each access, you're in the megabyte-per-second realm, and it will take a year to read a 20-terabyte disk. If you go to sequential access of larger chunks of the disk, you will get 500 times more bandwidth—you can read or write the disk in a day. So programmers have to start thinking of the disk as a sequential device rather than a random access device.

Tom White later says that - "MapReduce is a programming model for processing vast amounts of data. One of the reasons that it works so well is because it exploits a sweet spot of modern disk drive technology trends. In essence MapReduce works by repeatedly sorting and merging data that is streamed to and from disk at the transfer rate of the disk. Contrast this to accessing data from a relational database that operates at the seek rate of the disk (seeking is the process of moving the disk's head to a particular place on the disk to read or write data). Read more here.

My take is that SSDs are going to take a while to become an economically viable alternative to disks. Flash disks cost approximately $10/GB, and the OEM costs of good flash drives cost about $60/GB or more (source here). Compare this with the cost of disk, which is about $0.20/GB. So, we are looking at about 300x price difference here. So, I think, it's going to take while before SSDs become reality in storing terabytes of data. Until that time, we will have to use 50-70% empty disks to enhance striping-performance. So, if we were to use 50% empty disks, the cost of disks doubles for storing the same amount of data.