I have seen research articles and forum postings that demonstrate that SSDs are poor at reading large files: the larger the file, the slower the SSD compared to traditional hard disk drives. The difference with hard disk drives becomes apparent at medium size files, say 20KB. Does this mean that SSDs are suitable only for pages with lots of small page elements, such as icons and short pieces of text? Apart from price per GB, are SSD with the current level of technology suitable for web hosting environments?
The difference comes down to random versus sequential access. A traditional mechanical drive gets very high transfer rates only when its heads don't move much, like when it's reading one large file beginning to end.
Imagine 100 512-byte files stored in different places on the hard drive, with the drive having to drop everything and reposition its heads to read each one; with seek times of 10ms, that's an entire second spent retrieving 50 kilobytes of data -- an order of magnitude or so slower than it's rated speed.
A solid state disk has no heads to reposition, hence almost no seek time, so blows the pants off mechanical drives for random access. But individual flash memory cells are a bit pokey so a mechanical drive still beats them for raw transfer once its heads are in place. Of course read speeds can be improved in either just by throwing more money at them, more things running parallel in either gets better speed.
Both of these situations assume no cache, of course. Given enough memory the system will just cache everything after its first load to make all seeking and transfer rates irrelevant. And tiny files are, well, tiny, unless you have millions of them.
One thing SSD's are terrible for is frequent writing. Writing to flash is slow and inefficient, and gradually wears them out. Hard drives wear out too of course, but there's a world of difference between "this drive will last a couple years continuous use, no matter what you do to it" and "you could kill this drive in a week if you treat it badly enough". DRAM-based SSD's are free from this of course.
Thank you for your response. I have in the meantime found some sources that indeed make it evident that SSDs are not ready for hosting environments yet, ie there is no real business benefit, apart from the lower heat dissipation.
The environment that we were considering SSDs for is largely read-only, so web pages that are dynamically generated (PHP/SQL).