Less and More: A Buyer’s Guide to 4U ServersFactors to consider when making any 4U server purchasing decision.
In our recent look at 1U servers, we focused on compute density, the pursuit of packing the most compute cores into the smallest rack space possible. This slender form factor emerged in the years before the blade computing model and persists because blade architecture is significantly more expensive.
This time, let’s turn to 4U servers. The chief advantages of the 4U form factor are capacity for more disk storage and capacity for full-size add-in cards. As we’ll see, there’s also the potential for higher compute density, although this is a fairly new development.
Traditionally, 4U has been the go-to option for storage servers. More drives configurable into more robust RAIDs might require more processing power, which is why dual-processor (2P) platforms are the norm with 4Us and quad-processor (4P) designs are not uncommon. Similarly, four Gigabit Ethernet ports enable the transfer of data from these arrays to a large number of users without raising bottleneck concerns.
There are obviously many factors that should play into any 4U purchasing decision. Some of these will overlap with 1U concerns, and some will be specific to the larger form factor.
When looking at storage servers, how storage gets configured and the options tied to that configuration are clearly top priorities. Nearly all 4U servers feature some number of front-mounted, user-accessible drive bays. Typically, these will be hot-swappable. Some designs will accommodate 3.5” drives and others a higher number of 2.5” drives. Usually, the form factor of drive accepted can’t be changed owing to the storage backplane within the server matching one layout or the other.
Where storage subsystems begin to fundamentally differentiate is at the controller level. Budget-oriented boxes may only support SATA drives and the most basic RAID levels. More advanced chipsets and discrete onboard controllers may add support for SAS and more advanced RAID. Depending on the number and type of drives used, users may also have to keep a wary eye on the number of PCIe slots offered by the motherboard and the bandwidth supported by those cards. Discrete cards may be necessary just to offload RAID processing from the CPU(s), which may need that compute bandwidth for other tasks. Note that some vendors may offer a list of validated storage controllers for their 4U servers—always a good thing when trying to avoid potential compatibility issues.
As you look over our chart of sample 4U systems on page four, it’s obvious that Intel Xeon processor platforms fill the bulk of today’s server market. AMD may well be a more cost-effective fit in some cases, especially in data centers already standardized on Opteron systems, but buyers will find more options and SKU diversity on the Intel side. Similarly, expect there to be something of a price/feature gap between the older Intel Xeon 5xxx/7xxx platforms and the newer E5/E7 lines. There may be price advantages with the older tech, but be sure to weight these against the performance and power efficiency improvements in newer options.
Power supplies and cooling tend to be less frequently discussed than CPU, memory, and storage, but they may actually have a greater impact on ROI over the long-term. Redundancy is essential in any server scenario wherein maximum uptime must be maintained. Having an “extra” (N + 1) power supply running constantly obviously incurs more power drain and thus higher energy and cooling costs, so the efficiency of the power supplies is important. Simply noting 80 PLUS compliance is not enough. For example, an 80 PLUS Silver 115V power supply at 50% load is rated for 88% or better efficiency while 80 PLUS Platinum will ensure 92% or better. With heavy-draw systems running 24x7, every percentage point matters.
William Van Winkle has been a full-time tech writer and author since 1998. He specializes in a wide range of coverage areas, including unified communications, virtualization, Cloud Computing, storage solutions and more. William lives in Hillsboro, Oregon with his wife and 2.4 kids, and—when not scrambling to meet article deadlines—he enjoys reading, travel, and writing fiction.
See here for all of William's Tom's IT Pro articles.
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