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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.
The Six Dangers of Blade Servers
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.
This can be a limitation on technology but also is a limitation on leverage to obtain premium vendor pricing discounts in the future.
Take, as an example, a shop that wishes to run HP Integrity blades with their Intel Itanium processors today. They invest in blade enclosures and begin using them. In three years they purchase software that runs on Sun UltraSparc or IBM Power processors. In order to use blades each of these technologies will require their own brand of blade enclosure and will significantly increase the risk in a small shop that enclosures will not be able to be fully populated.
There is much more flexibility in technologies using traditional rackmount servers because each vendor generally supplies one set of RISC or EPIC-based systems and one set of AMD / Intel-based commodity systems. If you want more than that, blades will become quite difficult for a small shop to manage. I have worked firsthand with shops that use multiple technologies like this on a regular basis, making blades a most difficult choice today before considering potential future platform decisions.
The fourth danger is the shared backplane and other key components. A blade enclosure, while generally built with massive redundancy and with truly amazing design, still represents a single point of failure that must be considered.
If your enclosure fails you do not lose just a single server but as many as sixteen physical server platforms. With rackmount servers you can add redundancy simply by adding an additional server - typically one matching server for each server you need. With blades you have to have redundant enclosures for the same level of reliability.
Again, for a large enterprise this is trivial and obvious. For a small business the need to suddenly own dual enclosures for full redundancy will often result in simply foregoing that level of protection and increasing risk.
The fifth danger is in the cost of flexibility. Small IT shops may not often move their equipment around. The option is generally there, though. If a small business owns three servers and replaces one with a shiny, new unit the option is almost always there to redeploy the old server to another role - perhaps in a branch office.
With blades the old blades can only be redeployed in a location that has a blade enclosure matching the one from which the blade was pulled. This is a cost of lost opportunity late in the server lifecycle and often completely ignored in cost analysis of blades. If there is not a spot ready for an older server it is far more likely to be discarded in the blade model rather than redeployed. This is true unless the company is large enough to have many enclosures available all of the same generation and with available space ready to accept an older server.
The sixth danger of blades is the high cost of storage. Storage is a subject all its own these days with SAN, NAS and DAS as possible options. Shops of all sizes are moving to SAN and NAS quickly and with enough network storage in place this can alleviate much of the storage risk associated with blade servers.
Many shops, however, use circular reasoning and justify SAN because of the blades and blades because of the SAN. Taking a holistic view of the server and storage picture is crucial.
A typical blade server can house only one or two 2.5" SAS or SATA drives. This is far less than a typical rackmount server would provide as potential storage space.
It is common to find eight to sixteen drive bays available in popular 2U rackmount configurations - sometimes using 3.5" drives rather than 2.5" drives.
One popular and very cost effective 2U server can hold 28TB of low-cost storage on fourteen spindles. You cannot put this type of storage into a blade enclosure. Because local drive space is simply not available, blade server owners are forced to use minimal direct attached storage and use SAN or NAS instead, even when DAS would provide better performance and cost (otherwise) for that particular application.
To bridge this need most blade vendors provide storage blades - blade servers that act as tiny, low volume SAN devices and fit directly into the blade enclosure. These units are generally of rather low capacity, often just six drives, and rather expensive compared to other means of providing storage.
Additionally they use a critical enclosure bay, removing one of the potential slots necessary for a blade enclosure to provide server density. So an eight bay blade enclosure with two small storage blades would only be able to house six blade servers.
Obviously buying a blade enclosure does not mean that you have given up the ability to also use rackmount servers when appropriate. You can continue to mix and match. But to obtain the numbers necessary for a small business to cost justify the blade infrastructure often requires that purchases lean heavily toward blade servers to fill the enclosure(s) as densely as possible.
Much of the danger of blades is in the potential for lost opportunities. Small businesses especially function best and compete most strongly against larger businesses by being flexible and agile. Blades are the opposite of agile. They require large, upfront infrastructure planning that includes technological, physical and geographic lock-in.
Even if a business plans ahead and sees no obstacles to adoption this does not mean that opportunities will not be missed in the future. This could be caused by a lack of flexibility to adapt to changing business conditions effectively.
Once a blade enclosure is in place, purchasing decisions almost certainly are made based on the investment already made and no longer on simply what is best for the company. This doesn't have to happen but almost certainly will. Naturally, the existing investment needs to be protected.
All of this being said, blade servers can still make a lot of sense for certain businesses. Blade servers generally consume less power than their non-blade counterparts due to their shared system components. Be sure to consider the power consumption differences in the storage area, however, as blades push power consumption from the server to the SAN and can often be misleading as to where the power is going. A savings in one place is only valuable if the cost does not appear again in another.
Blades are easy to transport and relocate when enclosures are available. This can be a bigger factor than is obvious, especially when it means that there are several additional staff members capable of relocating a server. Almost anyone can lift and move a blade server.
A Virtualized Environment
When combined with a very aggressive SAN infrastructure, blades can be very beneficial to a virtualization environment. This combination gives the maximum cost and flexibility advantage to businesses large enough to leverage it.
The SMB market mostly consists of businesses for whom this would be very prohibitive, though, and this solution will continue to be relegated to businesses at the larger end of the SMB spectrum.
Virtualization will, in fact, reduce the number of servers needed by most businesses, making it even harder to justify blades to smaller businesses. Where previously a dozen or more servers would have been needed, today only two to four are needed to not only meet but to surpass earlier service levels.
If you can support adequate densities or get really aggressive vendor incentives then blades can be quite cost effective, if you calculate against your risks. Blades are always a little more risky, but if your cost is reduced significantly in buying them then they may be very much worth the risk in flexibility.
The cost of the enclosure is a key factor here. If your enclosure is free then suddenly the cost savings of a blade system can be enormous - especially if a large number of blades are purchased, providing really good enclosure density.
Blade servers are a great technology and show a lot of promise for the future. As enclosure lifecycles slow, new technologies emerge, costs are reduced, volumes increase and, hopefully, as vendor-neutral standards emerge Im confident that blades will become the de facto standard in even the smallest datacenters.
I see this as taking at least another market cycle before this will really occur. Most likely, in my opinion, it will be another five to seven years before the form factor truly displaces the rackmount server in general utility.
Scott Alan Miller is an IT Manager, Strategist and Engineer who has been working in IT for over fifteen years primarily in the financial, healthcare and SMB markets.