ned Productions Consulting

Technology musings by Niall Douglas
ned Productions Consulting
(an expert advice and services company based in Ireland)

Monday 17th March 2014 2.09am

Now I have my cloud node back and once again fully functional after I replaced and resilvered a failing hard drive in my ZFS array, I let it loose on catching up with changes of the past three months i.e. let it go full bore at syncing data over this supposedly 70Mbit vDSL internet which is the fastest I have ever had into my house (the Canadian connection was 54Mbit, St. Andrews just 6.4Mbit, and Kerry Pike was and still is a truly lovely 0.5Mbit). To date, he peaks at 7.9Mb/sec, no more, and in fact oscillates between about 6.5Mb/sec and 7.9Mb/sec. In Mbit terms, that is between 52Mbit and 63Mbit, so we're not quite at the point of saturating the connection yet.

So what's the cause? It's actually the cloud node: its 2.4Ghz dual core Sandy Bridge CPU is maxed out by the Linux KVM doing the downloading and decompression on one core, and the FreeNAS KVM doing the checksumming for ZFS and writing to disc on the other core, so for the first time to date since I set up this cloud node in late 2011 the CPU has become the bottleneck limiting everything else.

The big surprise really is that it hasn't happened until now: that Sandy Bridge CPU cost me €32 new back when it came out - that's right, it was the cheapest possible CPU at the time, and I think it's done marvellously running three fat KVMs and five thin VMs for the years since. Unfortunately, technology has overtaken it, but it just goes to show how linear growth Moore's Law has become: a bottom end €32 CPU from late 2011 is more than capable of running Linux and FreeBSD virtualised and pushing 100Mbit of data through both (it's the ZFS which drops throughput to the 50Mbit range, ZFS is very hard on the CPU caches especially when virtualised as ZFS talks to ~6Gb of RAM each time slice).

I'm very strongly minded to upgrade it to a Haswell 1220v3 Xeon CPU with a C224 chipset server motherboard as soon as financially possible. It should lop 40% off idle power consumption, important when a kWh costs €0.19; it adds ECC memory which is all important for stability under cosmic rays and substantially reducing the bitrot ZFS repairs every two weeks; bumps the CPU up by a third in single core speed and doubles the number of CPUs. Such hardware should carry me to the 200Mbit "vectoring" vDSL of supposedly sometime later this year here in Ireland which is probably as good as home internet will get for some years to come, so it's a future proofed investment. There is also an added side benefit: I sorely need a test machine capable of Intel TSX memory transactions as I am currently deploying TSX-enabled code which I have no idea whether it is fast or not, and that bugs me.

Roll on some financial security, that's what I say!