There are many hidden dangers inherent to the blade concept that are often overlooked and these hidden dangers can come back to haunt you long after you have committed to the idea of blades.
Before we look into blades themselves I want to discuss what blades are. According to Wikipedia: "Blade servers are stripped down computer servers with a modular design optimized to minimize the use of physical space. Whereas a standard rackmount server can function with (at least) a power cord and network cable, blade servers have many components removed to save space, minimize power consumption and other considerations, while still having all the functional components to be considered a computer."
It is important to define blade servers because it has become common, especially in the used server market, for resellers to use the term blade to refer to standard, 1U and 2U rackmount servers in the hopes of confusing customers new to the blade market.
Blades are a specific hardware category that requires the use of an enclosure and are not simply "small" servers. Blade servers use shared components in the enclosure, such as power supplies and remote management consoles, reducing the components necessary in each individual blade server.
The first danger of blades is cost. Blade enclosures are generally very expensive, even though blades themselves are often less expensive than their rackmount counterparts. In a quick price comparison of a large blade vendor's offerings, the enclosure was approximately $5,000 and could hold a maximum of eight blade servers.
Each blade was roughly $500 less expensive than the matching vendor's rackmount server of the same or similar specs. This means that a fully populated blade enclosure, at list price, from this vendor would cost $1,000 more than the equivalent computational power in traditional form factors. And every blade slot not populated would be an additional $500 deficit.
The cost of blades is not just a total cost factor. Blade enclosures, often holding eight to sixteen blade servers, need to be purchased up front. If you need enough servers to match the capacity of an enclosure this is not a factor, but if you are looking to buy only a single server now, you may be making a significant investment in proposed future server farm growth. This means increased risk as well as an investment against the time-value of your dollar.
Hardware cost is always a difficult number to nail down. Stated prices from the vendors rarely reflect reality and, as most companies know, dramatically lower prices are available if you demand them.
Ive known companies to get their blade enclosures for free, for example, which completely changes the cost equation of blades. But in the same breath one must remember that if a blade enclosure is available for free that serious discounts on traditional rackmount servers are likely also available.
So the list prices are often a good judge of relative prices even if not absolute ones. Your mileage will vary - so due diligence is necessary to create a cost analysis appropriate for your given situation and the deal that you receive from your vendor.
The second danger of blades is technological obsolescence. Unlike traditional racks, which have gone practically unchanged for many decades, blade enclosures are new and relatively dynamic. Several generations of blade enclosures have come and gone since their inception in 2001 and each subsequent generation, thus far, has required shops to replace their enclosures to support new blade servers.
This is a high risk if you are not buying servers often enough and in large enough quantity to justify the technology churn in the enclosures. This rate of change is slowing as the technologies mature, but risks remain. When doing a proper cost analysis of blade servers this rate of change needs to be factored.
The third danger is vendor lock-in. Traditional rack technologies are vendor agnostic. Most shops will mix and match not only servers but batteries, routers, switches, monitoring equipment and other gear into their racks. Blades are vendor specific. For a large enterprise this is of little or no concern. In a small shop with a limited number of servers it can be crucial not to give up the ability to use different vendors and technologies.