When is SSD the right choice for a performance boost

Question

I'm curious to know if there are any stats I could check in a performance/stats service like munin that would give me a feel for whether or not moving to ssd would have a significant performance impact? disk latency , disk ios etc.

Answer 1

As long as the primary reason for your poor performance isn't directly CPU-related (it would only be CPU-related if the CPU is... very overloaded by non-I/O-related operations), an SSD will always improve your system's performance compared to a HDD.

However:

• If your running programs use a very small percentage of your total RAM, and you have a lot of RAM compared to the size of your HDD, you already have, basically, an "SSD-ish" device due to page caching, once the computer has been booted up for a while. Example: if you had a 180 GB HDD and 72 GB of RAM, and your running programs only requested 2 GB of that 70 GB of RAM, the remaining 70 GB could be used to cache 70 GB out of the 180 GB on the HDD. The operating system would then intelligently choose which files to cache -- the ones most likely to be read from. In this bizarre and fairly unlikely scenario/example, an SSD would not provide a tremendous benefit except during system startup.

• If you plan to buy a very small capacity SSD (say, 64 GB or less), and you'll be writing and overwriting large files pretty much constantly -- as in a video processing server, for instance -- an SSD would wear out sooner than you might want. Usually, an SSD would last longer the larger it is, and the less you write to it per day (the "write load") relative to its size.

To sum up:

• The time from boot to usable system will be dramatically reduced by booting from an SSD instead of a HDD. This is more or less universally true.

• If you have many gigabytes of unused RAM in your system, you'll benefit less (though you'll still benefit) from switching from an HDD to SSD. On the other hand, if your programs use up most or all of your available RAM, an SSD will provide a more noticeable benefit.

• If your CPU is extremely busy doing general purpose computations from programs that are usually or always running, this situation will tend to "bottleneck" your system and make it hard for even an SSD's performance increase to be very noticeable. On the other hand, if your CPU has plenty of spare cycles, an SSD will provide a more noticeable benefit.

• One scenario where SSDs can be extremely useful due to their unique behavior is for database servers. DB servers benefit tremendously from having large amounts of RAM, and SSD as storage. This is a bit of niche, in one sense, because almost any other type of computer that isn't a dedicated database server (with a lot of IO operations per second needed) is not going to see such a spectacular improvement from an SSD.

Also, if cost is a concern for you and you still need to store a lot of data, you might consider having both an SSD and an HDD in your system. The SSD would contain the operating system, plus (perhaps) data that you need to access very frequently or rapidly. The HDD could contain large files that are stored for archival or infrequent access purposes, such as a large music or video library.

The degree of benefit you'll observe by adding an SSD to an existing system, or replacing a HDD with an SSD, will depend very heavily on your use case scenario. You may receive a breathtakingly tremendous benefit that extends the useful lifespan of your system; or, you may barely notice the improvement at all.