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Daily Archives: December 29, 2008

Storage

A Few SSD Comparisons

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So, I’m interested in SSDs, or Solid State Disks.  We’re seeing them come to the enterprise storage market, claiming that they can do the work of ten or more fiber channel platter based drives, albeit without the capacity.  I presume the reason that this works from a marketing perspective is that many applications need performance more than they do capacity, I know of several instances where we look at the number of spindles and only use a fraction of the storage space on each drive.  At any rate, now that major vendors are marketing them to the enterprise, it’s only a matter of time until the good stuff trickles down to the common folk.

Most enterprise storage is SLC NAND flash, which is inherently faster and more robust than the cheaper MLC that is commonly used un USB thumb drives, memory cards, and the like.  Both technologies have undergone improvements over the years, with vendors recently marketing a ten-fold increase in write cycles for both.  Even though the technology is improving, MLC is still the more consumer oriented device, and will be for the foreseeable future, because it’s cheaper to make at a given bit density.  While this may seem like it would relegate consumer SSDs to the lackluster performance seen on USB thumb drives, vendors get around this with their flash controllers, finding creative ways to write to arrays of flash chips, boosting performance enough to make MLC a viable option in the consumer storage space, which brings me to the main point of today’s article.

There are a lot of claims and counter-claims thrown about when it comes to SSDs.  Some say that they use more power, some say that they’re more power friendly.  One camp points to great read times, while another claims poor write performance.  So, being the curious individual that I am, I decided to run some of my own tests.  What follows is my own analysis of the products that I could get my hands on.  Be forewarned, these aren’t exhaustive tests, rather I focused primarily on my usage patterns and real-world situations.

Now to introduce the contenders:

  • Western Digital 2.5″ 5400RPM Scorpio, 160GB
  • Samsung 64GB SSD
  • OCZ “Solid series”, 60GB SSD

The comparison between the two SSDs is particularly of interest to me, because the Samsung was a $500 upgrade last February (of course I got a better deal than that), and the OCZ Solid SSD was recently purchased for $135. It’s their value line product and supposedly the lowest performing of their current line-up.

The two main areas I’m going to focus on are performance and power consumption.  I’m using two platforms, a Dell m1330 laptop, and a Lenovo ideapad S10, which is an Atom-based netbook. One special thing to note regarding setup, instructions from OCZ state to turn off AHCI or risk time-outs, pauses in your system.  Apparently they don’t handle (or need for that matter), some of the features of AHCI, such as Native Command Queueing.  I did not notice any difference on the m1330 with Vista SP1, but XP on the S10 definitely had long “WTF!?” pauses that were fixed by simply disabling AHCI in the BIOS. On to the benchmarks…

I’m beginning with the most relevant data captured, from iozone.  I’ll offer links to the full data, but one must be careful with interpreting the results, because iozone gives a complete overview of your entire platform, meaning that you see performance of processor caches, buffer caches, and disk. This can sometimes make it difficult to draw meaningful conclusions if one doesn’t understand all of the data. Another piece of information that will help you draw meaningful information from the data below, you can use the process monitor tool from SysInternals to view the transaction sizes that your various applications use. For example, my antivirus scanner reads files in 4k requests at a time, large files being copied with Explorer in Windows XP seem to be read and written 64k at a time, while in Vista files are read 1024k at a time and written 64k at a time. The behavior of the application, along with file sizes and their location on disk, are key in understanding the effects of the below data.

Many people have seen the phenomenal boot times of SSDs, and these tables highlight the reason. Comparing the older Samsung SSD to the Scorpio spindle, we see that random reads for the most common transaction sizes (4k-64k) are about 10 to 13 times faster. The OCZ SSD also shows this trend, and adds a big bump to sequential reads as well.  In exchange, however, we get slower writes, on the order of about 2 to 5 times, with random writes taking a big hit.  Still, it should be noted that random write performance isn’t particularly great even for the Scorpio at common transaction sizes.  All in all it seems to be a good tradeoff, especially considering that most data is write once, read many.

Another thing that this highlights is the benefit of defragmentation.  Many have asked the question “should you defragment an SSD?”, and the common wisdom is that defragmentation isn’t necessary with SSDs.  While they should indeed be limited in order to preserve the (currently unknown) longevity of the flash, one needs only to look at the performance between random and sequential to see that even SSDs benefit from defragmentation.  Some people are concerned about the write lifetime of flash, and while manufacturers try to put people at ease with their various wear optimization techniques, the reality is that most of these devices are too new to have a proven track record either way.  For the record, I’ve had my Samsung for about a year now, have beaten the hell out of it as far as writes, and haven’t had any issues yet ;-).

full iozone data –  xls csv

Here’s another look, this time by a simpler benchmark from ATTO on the XP netbook. I won’t go into too much detail here as it’s more of the same, but you can view the results by clicking on the thumbnails below.  Note that if one were to only use this tool, one might not see why the samsung SSD is subjectively much faster in day to day use than the Scorpio drive.

ATTO- WD Scorpio 160GB

ATTO- WD Scorpio 160GB

ATTO Samsung SSD 64GB

ATTO Samsung SSD 64GB

ATTO OCZ Core series 60GB

ATTO OCZ Solid series 60GB

Next up, a real world scenario: virus scan. This should show a huge improvement when moving to SSD, according to the iozone results. Some of the information will be sequential, but most will be random.  On top of that, as I mentioned, the virus scanner I’m using seems to read files 4k at a time. The setup is Avast! Antivirus, running a standard scan on Vista SP1.

The results speak for themselves. The iozone data seems to translate into real-world performance.

Now for battery life. I performed two tests, one was watching an xvid encoded 480p movie from the hard disk, the other was pretty much idle, with a script writing a small amount of data to the hard drive every 30 seconds.  The movie was chosen because it did a good job of generating  a constant stream of i/o (64k at a time) while not being absurdly taxing on the disk like running a benchmark might, a good real-world scenario. Actual results should in theory end up somewhere between the two benchmarks.

The m1330 loses a bit of life when switching to SSD, about 8 minutes. However, with the S10 it seems to be a wash. There are too many differences between the two platforms to pinpoint the cause. It could be due to the more aggressive performance settings I have in the m1330’s power options, could be a hardware difference, or even XP vs Vista.  All we can really say is that the mileage isn’t due to the disk alone, but how the platform reacts to it. Your mileage will depend on your platform, but the difference isn’t much.

Again, we see conflicting results. The S10 likes SSDs, while the m1330 doesn’t. I searched through the power options, and there were a few differences on the m1330 in regards to processor frequencies, but the hard disk settings were the same between platforms.  I have a hunch that the S10, being a smaller, lower wattage platform overall, will be more sensitive to the actual power consumption of the drive. Make of it what you will, the differences don’t seem to be all that much either way.

In summary, it seems that SSDs, in their current incarnation, offer a large boost to read performance in exchange for a medium-small cut in write performance. There are differences in battery life, but the differences are relatively small and differ between platforms. I would like to get my hands on some of the higher-end SSDs such as the intel x25, but until the prices come down, I think that comparing these (now) budget SSDs has been a useful exercise.