Since the early days of blade server architectures, the larger IT customers have adopted this higher density or converged approach for their compute resources. This caused the rackmount server to be delegated to specialty-use cases and smaller customers. Given many of the new solutions and products being released by vendors in 2013, I think the rackmount server is primed for a comeback.
There are bound to still be many customers that are using rackmount servers today for many reasons, I’m going to focus this post towards customers that are currently using blades. Hopefully this discussion with open up some good discussions on how a rackmount platform may offer more flexibility in certain scenarios over a blade server architecture. This will be the inverse of the how blades might simplify a design that has been occurring over the last decade.
To get things started, I will discuss some of the more interesting solutions that might sway a design towards a rack server model over blades. This should help paint the picture of how the two platforms would contrast.
Within this use case the requirement would be to offer upgraded graphics capabilities to applications or users. Since the typical server is equipped with a very basic video adapter, this limits the use cases to server workloads or basic knowledge worker-type workloads. In the past, one of the common methods was to equip a rack server or to purchase a workstation type blade server that had an upgraded video card. These options were both limiting in flexibility and costs.
Recent video technology from Nvidia in their Grid offering and support from Citrix and VMware now allows for these more powerful video offerings to be presented to end users. This allows for use cases that would typically now be candidates for being centralized into the data center to now be accommodated.
Since these types of display adapters are currently only being offered on a PCI card, this heavily sways the discussion towards rackmount servers. By using a rack server the option to potentially configure each server with multiple upgraded display adapters is also an option.
I don’t see this changing anytime soon unless the blade server vendors partner further with video adapter manufacturers to create an option to provide the upgrade video options in an onboard offering. This would likely require the server vendors to create new server models to allow for this solution. I have not heard anything about this yet but it could be happening in the basement labs at HP, Cisco, or Dell today.
The next use case is becoming very popular and in the last 18 months there have been a number of third-party vendors and VMware release and announce offerings around this space. I recently wrote a Petri article about server side caching that you can read for more details. The general idea here is that local solid state or flash disks (SSD) would be placed into the server, and the solution would utilize the flash as a local cache layer. This would accelerate the reads of VMs and possibly the writes.
This type of solution is not impossible with blade servers but is a bit more limited. I think nearly almost every blade server offer by a major manufacturer offers the ability to configure with one or two local disks. These could be SSD and used for this local caching layer. But you would be likely limited to a maximum of two disks, and this might be limiting based on your VM density or data set size of your workloads. In this thought most rackmount servers offer typically from 6 to 20+ bays for installing local disks. This greatly expands your options should you need the additional capacity.
The other popular option here with blade servers is the ability to use a PCIe flash card solution. This type of flash is faster and offers lower latency than your typical SSD drive that is accessed via a SATA or SAS controller. With a rack server the ability to access several PCI slots opens up the options. Don’t get me wrong – there are still some limited offerings in this space that allow for a FusionIO offering to be configured into a blade server via a Mezzanine slot. But this solution will be limited in the capacity options and the blade servers that support it. Also you may be using up a valuable mezzanine slot that may be needed for network connectivity.
The last use case that I wanted to talk about was the idea of using local server storage and unifying it into a shared storage layer. An example of this type solution would be VMware VSAN, although there are other third-party products coming to market. At its basic level, VMware VSAN is using a single SSD and multiple spinning disks in each server. These disks are used to create a storage layer across the hosts that can be used as a datastore.
These type of solutions are using flash storage or a cache layer to offer all flash type performance, and then it uses the spinning disks for capacity. This type of storage option might not be right for all workloads, but it does make sense for some. VSAN will offer good performance but will lack many of the more advanced storage features that many customers expect from shared storage arrays.
By now you are probably guessing from the previous use case that the blade servers are going to be pretty limited in supporting this type of solution due to their small number of local disk bays. But this is where many rackmount servers shine, because there are models from every server vendor that can offer some incredible local disk density. This would allow customers to design storage for a use case that is localized to the server and is able to offer a high level of capacity and performance. This technology space is heating up fast with VMware jumping in with their VSAN announcement at VMworld. In my interactions with customers there is already a lot of interest in how this type of storage might be used.
Over the last five years or so I personally have worked with mostly blade servers for customer designs, but given these new technologies I recently find myself spending more time on how rack servers might fit in. If you have any insight on this discussion drop us a note in the comments and share with the community!