The comments on my last post on the new Dell servers were asking for pictures – so if you’ve ever wondered what your website ‘physically’ looks like, here’s a bit of insight!

This is a Dell R720; we use these as general-purpose storage servers wherever we need to store a lot of data and get at it reasonably quickly. They come in a variety of configurations, but the one that we’re looking at today has space for two Xeon CPUs, can take up to 8x4TB HDDs, up to 512GB of RAM (although we’d never put that much in a storage box – 32GB is usually enough for decent amounts of disk cache).

So, let’s dive in. At the front, we’ve got 6x3TB HDDs and two spare slots for future expansion. These plug into a backplane so that you can swap them out without having to open the chassis or shut down the machine; as they’re one of the few components that physically move, they’re one of the most prone to failure so this is really important! This server will use RAID-10, so that when a hard drive does fail, it can be replaced with zero downtime and zero data loss, and only a tiny performance hit while the RAID array repairs itself. We’re using Enterprise SATA drives in this server, which give similar performance to standard SATA drives but are designed for 24/7 use over many years. They’re more expensive, but worth it – we see a much lower failure rate with these disks than the rated values for home-use drives.

Just behind the disks are are the fans – in a high-density rack, airflow and cooling are very important, so these are absolutely crucial. These are also hot-swappable, but they rarely fail. Like almost every component in the server, though, we do monitor the fans and can arrange a swap very quickly.

Next up is the RAM – this is similar to the RAM in a home PC, but faster and a lot more expensive, on account of it being fully buffered. FB-DIMMS offer higher performance and much higher reliability by adding a ‘buffer’ between the CPU and the RAM itself, which means that the CPU doesn’t have to wait for the RAM to become ready to read or write, and error correction/re-sending can be handled in the RAM rather than by the CPU, or being ignored.

Under this heatsink is a 6-core Intel Xeon CPU that’ll make light work of the processing. You’ll note that it’s nestled in amongst the RAM; there’re two reasons for this: firstly, this is right in front of the fans (note that little flash of orange in the back of the photo?) and the RAM and CPU are the components that produce the most heat, but also the RAM and the CPU are in constant communication, so to minimise latency and signal loss, motherboards typically place the two as close together as possible.

Server CPUs are designed to deliver performance when it’s needed and to drop their power usage when it’s not, and by using a combination of multi-socket and multi-core technology, we can gain maximum performance without pushing up the power bill too much, and without producing too much heat. The strange shape of the heatsink is due to the component sheath that isn’t shown here – this channels air around the chassis to maximise cooling efficiency. Towards the back of the chassis is the RAID card – this controls all the disks and relieves the CPUs from having to do any work relating to i/o management. It also has a cache to help speed up both reads and writes, and both a battery and flash storage to preserve the cache in the event of power failure.

All our new customer-facing servers have dual hot-swap power supplies, which means that any interruption to one of the power supplies or a component failure doesn’t take the server down with it. R720s come with much more efficient power supplies than previous generations – R710s came with PSUs at either 800W or 1kW, whereas the R720 is happy with 495W.

And finally, at the back, are all the connectors – 4 network ports (we run several independent networks for different purposes, and oftentimes servers need to reside on multiple networks – hence multiple NICs), VGA and USB for connecting a keyboard and mouse on the rare occasions that we need to physically attend to a machine, and a serial port. Servers are one of the few remaining applications of serial connectors, but they’re very valuable as they give us a means of accessing a server even when it’s on the brink of crashing.

So that’s it! In a few days, this server will be off to one of our datacentres to be part of our shared hosting platform; next time you set up a Heart Internet hosting package, your data may just end up on this very server.