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Partitioning in network, storage systems (Part 1)

Posted: 25 Sep 2014     Print Version  Bookmark and Share

Keywords:server virtualisation  partitioning  Network adaptor  operating systems  NIC 

As the server virtualisation technology has been widely adopted over the past few years, I have noticed a proliferation of partitioning technology across all layers of the technology stack – from the server to the network and storage layers, all the way up to the application. And, while the concept of partitioning (the act of dividing something into parts) is simple, the capabilities and features that come from the use of this powerful design pattern are fairly complex.

In this two-part series, I will discuss some key places where we see partitioning technology utilised and explore some of the impacts and implications that these technologies have within the data centre.

Partitioning
Partitioning has been a fundamental concept within computer science for over 50 years. Early mainframe computers leveraged partitioning to share compute, memory, and storage resources among different users on the system. And in the late 1960's, IBM figured out how to partition a single physical machine into multiple virtual machines, each of which could run an independent copy of an operating system.

Although it took more than 40 years for the industry to commoditise this concept of server partitioning, once it took hold, server virtualisation instantly became a pervasive technology within data centres all across the globe. It is interesting to take a look at the impact that this trend is actually having on the technology ecosystem.

One of the first sets of problems that server virtualisation provoked was related to device sharing. As expected, when you introduce the concept of sharing resources among different users, there is an obvious concern over both security (is my data secure?) and performance (How much slower is my IO going to be? Can another user take all the bandwidth on the device?). These concerns have driven major changes in both the network and storage ecosystems.

Figure 1: Network adaptor with NIC partitioning.

On the network side, the industry response was two-fold. The first was to develop a specification (Single–Root IO Virtualisation or SR–IOV for short) for allowing the bare metal operating system (the hypervisor) to partition the physical network interfaces into separate "virtual" interfaces, each of which would be treated fundamentally like it was an independent network end-point.

The value of this approach was to create an industry standard way for PCI-based devices to effectively partition a physical network port. This approach to partitioning requires that the bare metal operating system take an active part in configuring these devices.

The second response was that the leading NIC vendors began to provide proprietary partitioning capability directly in their hardware (figure 1). These multi-channel capabilities allowed a single physical network port to look like multiple physical network ports to the operating system without the need for the operating system to configure the device – it is discovered by the operating system just like a standard NIC port.

Of course you still need to configure the virtual ports, but in this case the configuration is done through the BIOS or special management software provided by the NIC vendor. Some of the vendors even provide quality-of-service capabilities to control and monitor the amount of traffic on that interface, making it feel like an independent device.

In the end, both of these technologies provide the same high-level benefit, which is to allow server virtualisation software to carve off a "virtual" NIC when it needs to provide an isolated "dedicated" network end-point to a guest operating system.

This use of partitioning at the network interface level has had a substantial impact on the data centre network. The proliferation of network end-points has caused a dramatic increase in number of MAC addresses (and IP addresses) that have to be managed. It has put pressure not only on how we manage these devices but also on network infrastructure itself.

Switches have had to extend their models to support this one-to-many paradigm. Configuration items that were done once for a given physical port now have to be done potentially multiple times on each port (one for each virtual NIC). This puts pressure on the scalability of the switches, including their internal table limits.

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