Review: Dell R815 server makes heavy virtualization light on the wallet

The Dell PowerEdge R815 and its four 12-core AMD Opteron CPUs want to run many, many virtual machines, at a much lower cost than Intel multicore

There's something different about watching a server process list spanning 48 logical CPUs. It invariably engenders a feeling of raw power, not because each CPU is fast but simply because there are so many of them. Those 48 logical processors show you just what the Dell PowerEdge R815 has to offer: It's a server that needs lots of work to do.  

It's a little difficult to measure the Dell R815 and its four AMD Opteron 12-core CPUs against its competitors. The R815 doesn't have the clock speed of an Intel Westmere-EP CPU, but it does have twice the number of physical cores. It doesn't have the extended RAS features present in the Intel Nehalem-EX, but it does have a slightly faster clock and 30% more cores -- and a significantly lower price. 

[ Which is the better blade server? See InfoWorld's "Blade server review: Dell, HP, and IBM battle for the virtual data center" and "InfoWorld review: Cisco UCS wows." ]

So rather than directly compare this CPU -- and this server -- to its Intel competition, it's best to look at it from a real-world point of view. And that view is of a box screaming for a virtualization workload while somehow avoiding a budget-destroying price tag. The R815 even includes nice extras such as sizable internal storage and array controller options, redundant SD card slots, and enhanced iDRAC management tools. Given that an R815 with four Magny-Cours CPUs costs thousands less than a comparable server with two Nehalem-EX CPUs, it delivers better bang for the buck for sufficiently multithreaded workloads. (See my comparative test results, "AMD Opteron Magny-Cours versus Intel Xeon Nehalem-EX.")

Virtualization value leaderThe Dell PowerEdge R815 is a beefy representative of the Dell PowerEdge server line. It's a 2U chassis holding four AMD Opteron 6100-series CPUs and 512GB of RAM. It houses up to six 2.5-inch SAS, SATA, or SSD disks, and it has four built-in copper gigabit NICs out the back. Coupled with the expected redundant power supplies and the relatively unexpected redundant SD-card options, it brings to mind one of those massive dump trucks that have eight-foot-high wheels. 

While the maximum number of cores you can fit into an R815 is 48, you can opt for less expensive CPUs in the AMD Opteron 6100-series line and run with two or four eight-core CPUs. At the low end, this means you can pick up an R815 with four eight-core, 2.0GHz Opteron 6128 CPUs, 16GB of RAM, and two SATA drives for around $4,725 at the time of this writing. Choosing the crème-de-la-crème 12-core, 2.3GHz Opteron 6176SE processors will run you another $1,000 per chip, which is still far cheaper than the Intel alternative.

How many single-purpose workloads can make effective use of a box of this size? Not many. Heavily threaded applications, big database workloads, and data warehousing builds fit the picture, but a fully loaded R815 isn't likely your first choice for a Microsoft Exchange server or Web server. However, the R815 most certainly is a box you'd want to use to run a ton of virtual servers on.

Virtualization hammers RAM, I/O, and CPU, in that order. Most virtual machines in most VMware farms require surprisingly modest CPU resources, but they need as much RAM as they can get -- and a fast pipe for access to storage and client workloads. These things the R815 can definitely deliver. By spreading virtual machines across such a large logical CPU count, you're essentially immune to overextending CPU resources, and with up to 512GB of RAM, you'd be hard-pressed to exhaust that either. The AMD Magny-Cours CPU doesn't extend to the 1TB of RAM that a Nehalem-EX server can deliver, but there aren't many cases where 1TB of RAM is a realistic expenditure in this server classification.

In short, the R815 can deliver as much virtualization horsepower in a single chassis as you might expect from three or four 1U servers. The four 1G copper Ethernet interfaces pose a potential bottleneck, but if you arm the R815 with optional 10G interfaces, there's no concern about network I/O to support all those VMs.

Twin SD cards and iDRAC6While the R815 does have a maximum raw local disk capacity of 3TB in SAS or SATA drives, you don't need disk at all for some applications. The R815 contains a matched set of SD card slots inside the chassis. These slots can accommodate standard SD flash cards, and they are configured for redundancy. It's not a RAID mirror, but whatever's written to one SD card is written to the other. Thus, it's possible to install embedded hypervisors such as VMware ESXi straight to the SD cards and boot the server without any local hard drives whatsoever, reducing heat production, power consumption, and the problems associated with spinning disk.

I found the performance of the SD cards to be sluggish compared to hard disk, but that's a given. The fact is that once the server has booted an embedded hypervisor, there aren't many reads and writes from the SD cards, so there's no realistic performance degradation. The redundancy of the SD card slots also protects against the failure of one of the SD cards. You can even select which card to boot from.

Although not unique to the R815, another compelling element to this server is the availability of the iDRAC6. It comes in three flavors, with the low-end Express unit offering a surprisingly capable lights-out administration package. Express includes integration with Active Directory for authentication, serial-over-LAN, boot screen and crash screen capture, and server power control, but lacks remote console capabilities and a dedicated network interface.

The Enterprise version adds these plus support for centralized management via Dell's OpenManage tools, remote file sharing, and virtual media support. The vFlash version includes everything the Enterprise version does and offers up to 8GB of local SD-based flash storage that can hold, for example, a fresh install version of the server OS, rescue images, or anything else that might be necessary to assist the server or recover from failure.

The Dell PowerEdge R815 won't be the fastest server in your data center as measured by core clock speed and single-threaded task completion times. But it will carry a significantly heavier load than the speedier boxes simply by the sheer number of available cores. The R815 would be right at home in a large virtualization farm or used as a warm-site virtualization host that can take on a heavy load if something happens to the production data center. It's a big box, but it'll also cost a lot less than you might otherwise think for a quad-socket server.

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