Sep 15, 2011 8:48 AM
Written September 2011.
SSD's are hot. Everybody talks about them and they are rumored to be the non-plus-ultra for performance gains. I write this to create a more realistic view on where we are now with SSD's.
SSD's have the reputation of being very fast, much faster than conventional hard disks. There are many reports on the internet that investing in SSD's will give you huge performance benefits and that is the explanation why so many people consider SSD's a must have for the ultimate performance experience. Unfortunately - and this is especially true for video editors - this is mostly a hype and not a wise decision.
Let's start with the basics.
They are physically small, have no moving parts, are quiet, cool and expensive per GB. The small physical dimensions mean that you can easily fit 4 SSD's in a single 5.25" bay. Because there are no moving parts they are quieter than conventional disks. They also operate at lower temperatures than conventional disks, which is a distinct advantage in a crowded system. Average access time is negligent in comparison to conventional disks. SSD's are not as susceptible to fill-rate degradation as conventional disks. (Conventional disks tend to show performance degradation when filled for more than 60%. Not so for SSD's). But there is the cost aspect and the reliability question.
But the most important question is performance. Does it justify the extra cost for the increase in performance?
Currently, the price per GB for a SSD of the latest generation is generally around $ 1.40 - $ 2.00, depending on the model, capacity and brand. A conventional disk is around $ 0.05 - $ 0.06 per GB and that means a SSD is around 30 times more expensive per GB. Is it worth the difference?
According to many, the answer is yes, it is worth it, but I beg to differ. Proponents of SSD's claim that the transfer rates of SSD's with figures of 500 MB/s are way faster than the 120+ MB/s of modern conventional hard disks and that justifies the extra cost. If this were true, why don't we see those performance gains in our benchmark? What is wrong with these claims of unprecedented speeds?
Manufacturer's claims of IOPS - which are irrelevant for video editing - and sequential transfer rates are based on highly compressible data in 4K blocks, something that video data are not, because they have already been heavily compressed. It boils down to writing only 0's and compressing those 0's to achieve the claimed transfer rates of 500 MB/s, but effectively only around 30 MB/s are transferred. If you were to test effective transfer rates using CrystalDiskMark, which uses random data to benchmark, the compression is far less, because it is random, and then the effective transfer rate of SSD's is reduced to something in the order of 200 MB/s. With video data, the effective transfer rate could well be even much less because of the heavy compression that has already taken place during the shoot.
Interesting to see, and I do not know the answer, whether a heavily compressed codec like AVCHD would show lower transfer rates than less compressed codecs like P2-Intra or 50 Mbps MPEG2.
This is one of the most discussed issues with SSD's. On new SSD's the write speed is almost as good as the read speed, but when using that SSD for a longer time there are serious performance issues while writing data to a SSD. Even with the latest generation SATA3 / Sandhurst SF-2281 SSD's, write performance can easily drop by more than 60% despite the TRIM function. This effectively means in the best case scenario, that a SSD with a claimed transfer rate of 500 MB/s, which delivers less than 200 MB/s read speed with video data, can only deliver 80 MB/s or less write speed when used for some time. That is not too impressive in comparison to conventional disks at a fraction of the cost and less than a simple raid0 with two conventional disks on a ICHR10 on-board controller attains.
If TRIM is not working, the write degradation is even worse and you may count yourself lucky to attain write speeds of 50 MB/s or less. Unfortunately, most SSD's firmware in combination with raid controllers currently have the nasty side effect of disabling the TRIM function, so raiding SSD's is not a serious choice for raid configurations.
The only way to correct this write degradation is by performing a secure erase, which means losing all the data on the SSD, not a nice perspective for anybody, but most of all for notebook users. Are your backups current?
NAND memory is susceptible to ageing and most SSD's calculate their lifespan in data transfer values. In a worst case scenario this usually means you can rewrite the complete contents of a SSD around 125 times, before the NAND memory is no longer reliable/useable. Not many people would try that and for a boot disk this means a very, very long time before the useful life of a SSD is at an end, but for video editors it is a different story.
The bottom line on SSD's at this moment of writing
- They are the way to go in the future, but not yet.
- For OS & program disks they are great, provided you set up Windows to not use the SSD for temp storage. They can easily shave off 3 or 4 seconds from your usual boot time of 60+ seconds, depending on your configuration. (Did you notice any sarcasm in this statement? You should.)
- They are a waste of money for video storage and do not deliver any performance gain, because of the compression that has already taken place with the video material and that lowers the transfer rates significantly.
- The faster loading of programs, which is often used as an argument for SSD's, is usually limited to 1 second per program or not even be noticeable.
What would you rather have at this moment:
a. 8 TB of net storage with conventional disks for around $ 400 with a sustained transfer rate of 1000 MB/s, or
b. 2 TB of net storage with SSD's for around $ 3000 with the same transfer rate?
Just my $ 0.02