It's pretty well-known that SSDs are poised to make a big splash in enterprise storage environments, and by the same token most storage experts recognize that not all situations call for a wholesale dumping of hard disk technology.

But as they say, the devil is in the details, and in this case those details include exactly where SSDs make the most sense and where they are best avoided.

Pam Baker over at Enterprise IT Planet does a good job of laying out the pros and cons of SSDs. On the pro side, she lists their energy efficiency, low latency and even their durability in harsh conditions. The cons include upfront costs, life expectancy and the fact that the technology is only just beginning to prove itself in enterprise-class environments. And for those who are hoping to slowly implement SSDs so as not be too disruptive, recognize that the performance gains the technology brings will extend way beyond storage infrastructure, impacting network, server and even desktop systems as well.

When you get right down to swapping out hard drives for SSDs, however, there are a number of things to keep in mind, says Marcus Schneider of the Storage Networking Industry Association's European wing. Among them are that HDDs still rule in terms of price/GB, have better write performance and, although slower, are more likely to last longer in high I/O environments. SSDs, meanwhile, are cheaper in terms of cost/IOPS and can deliver equal performance regardless of what form factor they are housed in, leading to highly dense storage systems. Neither solution is idea for all storage situations, so the trick will be to determine which one offers the better performance on a case-by-case basis.

For a handy guide on the relative merits of some of the more popular drives out there, check out this chart that Microsoft architect James Hamilton got from AMD. The Intel X25-E, for example, delivers upwards of 7,000 random IOPS/second and has a capacity of 64 GB for about $800. Go over all drive specs carefully, he says, because the last thing you want to do is find yourself with limited capacity or limited I/O performance by dropping the wrong drive in.

One thing that might help SSD deployment decisions is a set of professional standards that can be used to verify manufacturers' claims, says Thomas Coughlin, an analyst with Gerson Lehrman Group. SSDs use a different storage architecture than hard disks, so it's imperative that the industry devise SSD-specific metrics and test methods to evaluate things like endurance and reliability in real-world enterprise environments. JEDEC and the SNIA are both working on the problem, but until the situation gets resolved, enterprises have little to go on but vendors' own performance claims.

SSDs and HDDs are likely to share enterprise networks for quite some time, so it's imperative that they both stake out their own unique roles. Fortunately, there are enough differences in the benefits they provide and the performance levels they offer so it should be easy to keep the overlap to a minumum.