Mark Sutton

Chief Technology Officer

As CTO Mark defines the technical strategy for CatN, designs and builds our key IT assets and engages with the IT community to communicate the CatN vision. You can find Mark on Google+

Cloud transition: how can you move from over subscription to capacity utilisation?

The journey of many businesses from a heavily over subscribed infrastructure solution to the flexible, scalable world of cloud we are in today is a very interesting one. It is still possible to draw parallels between what is now considered to be a highly inefficient approach to building IT solutions, and the practises we still see from some IT suppliers.

In the 2000s it was incredibly common to find an over subscription of hardware when looking at consumption by real workloads. On top of that there would often be a further over subscription for peak periods, especially in e-commerce. This created a double whammy of very high expenditure levels for a given amount of business. The irony was that capacity and spend are relatively interchangeable due to them being commodity infrastructure items.

In the second half of the noughties there was a shift away from the over subscription of hardware. The reason was virtualisation. This allowed businesses to combine and consolidate all of their work loads onto as little hardware as possible. Unfortunately the fact remained, it was still necessary to maintain an overhead of capacity which meant an over subscription for peak periods.

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CatN goes to CentOS Dojo Antwerp

It’s no secret that we use a lot of CentOS at CatN, in fact we have deployed thousands of instances over time on both physical and virtual machines, and we have 4 Red Hat Certified Engineers (soon to be 6) on staff.

As a company with deep expertise and experience with CentOS it makes complete sense that we understand where our software comes from. You only have to look at the state of our food chain to see that interest in your upstream makes a lot of sense. At the end of the day we have to trust the food [software] that we eat [install]!

Getting to events like this is a great way to get a feel for a community, meet people and potentially find a way to contribute back into the ecosystem as well. What’s not to like about that?

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T minus 1 year and counting – is your router about to go boom‽

In approximately one year’s time, the global routing table will grow past the magic 512000 prefix mark and render millions of routers unable to carry the global routing table. If you operate a router with BGP on a public AS number, you should probably read on.

Every so often seismic events happen in the tech world, such as the Millennium and leap second bugs, hash collisions and IPv4 depletion. All of these events have the ability to wreak havoc far and wide, but before I go into the detail of what’s about to happen, let me first give you a bit of background.

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Speculations on the Facebook PHP Rumours…

Rumours abound this weekend, and as usual in such matters, details are thin on the ground. Did that meeting really happen? And who is this lonesome coder supposedly re-writing PHP for the last two years? Is it a new runtime or a compiler? Someone knows, and for sure something is afoot, but what is it?

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Securing mod_php – without the vasectomy

In it’s most typical setup, Apache 2/mod_php is not secure enough for shared virtual hosting.

With the typical mod_php setup, a rogue webmaster or bug in a single PHP script could compromise every script and configuration file for every site hosted on the server, no matter how security conscious the developer.

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OpenVZ forced umount of lustre mount problem

Recently we managed to find an answer to a quite worrying lustre problem that has been bugging us for some time. Every now and then on servers running OpenVZ containers that make use of lustre filesystem we would see a log entry in /var/log/messages saying:

kernel: Lustre: setting import lustre-server-MDT0000_UUID INACTIVE by administrator request

followed by a number of broken mounts/fs errors inside containers running on the server that the log entry appeared. In effect, all the containers making extensive use of the same lustre server would stop working properly (for example, apache serving sites from lustre mounts would start spawning processes all of which would be unsuccessfully trying to read data from the mounts).

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Adventures with Lustre

For the last few months we’ve been busy integrating, testing and tuning Lustre for use on our hosting platform. I thought I’d share some notes…

Lustre is most widely used in HPC settings and there seem to be relatively few operations using it in conjunction with web servers and virtualisation. Reading through the wiki and mailling lists it soon becomes clear that Lustre has not been designed with small files and high metadata request rates in mind. Read More

Preparing Procurve Switches for Production

We recently took delivery of some new Procurve 5406zl switches for our Cloud platform. As with any new device being attached to the network there are quite a few tasks that must be done before it can be plugged into the production network. Naturally we document this internally but this time the process was quite interesting so I thought I’d blog it as well. Read More

.htaccess revisited

About a year ago Dawid posted about the performance of .htaccess files. We decided to revisit these tests to compare the performance of .htaccess files on local disk and network filesystems. The network filesystem we used was Lustre, chosen partly because we are doing a lot of testing with Lustre at the moment but also because of its’ known issues with metatdata and small file performance.

The test setup is a Dual Xeon 3.2GHz server with 4GB of RAM and a gigabit network connection to the testing and storage vlans. We installed the latest version of our Apache 2.2.11 build with mpm-worker and two vhosts. One vhost has a DocumentRoot on local disk, the other has a DocumentRoot on Lustre storage. Read More

Getting to know Lustre

Lustre is a complex cluster filesystem aimed at super computing clusters, offering scalability to many Gigabytes per second and Petabytes of raw storage. We’ve been testing it for some time as a base filesystem for virtualisation and I wanted to share some notes. Read More