Wednesday, February 22, 2012

Goodbye Cable TV...Almost

I've been working for the past few weeks to prepare for the severing of relationships with our current cable TV provider -- signing up for Hulu, building a HTPC (Home Theater Personal Computer, for the uninitiated), etc.  Last night, I completed the last few steps -- powered down the TiVo and removed the CableCARDs in it.  Then, this morning, I called to cancel my account.

Except I didn't do it.

As I had expected, I was passed over to the "retentions" department and I was given a few options to entice me to stay.  What I wasn't expecting, however, were the plans that didn't have any promotional pricing, and pretty reasonable prices at that.  I ended up scaling us back to the "bare bones minimum" plan that only gives us the network channels plus a smattering of basic cable channels (Discovery being the only one he listed that we watch with any frequency).  This plan is about $21/mo (probably $25 after taxes), which compared to the $98 we had been paying before (plus the $13/month going to TiVo, which is also going to get cancelled in favor of the HTPC), is still a pretty reasonable savings -- about $86 per month, or just over $1000 a year!

I'm not viewing this as "caving in" to their attempts to retain me as a paying customer, and part of me was expecting this to be the end outcome anyway, for the following reasons:

  • While I have managed to locate online alternatives to almost all of our shows, the ones we like from Discovery do not really seem to be online anywhere, other than paying per episode from Amazon.  Plus, Discovery can be one of those great put-it-on-and-forget-about-it channels, for example when I'm sick on the couch.
  • Part of my plan had included getting the network stations "OTA" (over the air) with an antenna.  Unfortunately, I don't yet have an antenna in place, nor do I have the structured cabling installed yet to get the signal from it to the TV.  Since this new cable plan has no commitment period, this can act, if nothing else, as a stop-gap until we can get the antenna set up.
So, we shall see how this works....

Thursday, February 9, 2012

XenServer Network Bonding

I've just had a bit of a learning experience with respect to Citrix XenServer and what it refers to as network bonding, and thought I would share here.

All of what I am about to say comes with the disclaimer that I am not a network engineer, but rather a server engineer, so my networking terms may not be 100% accurate.

I've been working to deploy a new XenServer pool here at $WORK recently, and we've been working under the assumption that we would connect it to our new datacenter networking standard, which we refer to locally as a "virtual chassis" -- two in-rack switches "stacked" together connected independently via 10GE to two stacked aggregator switches and network traffic tagged with standard 802.1q vlan tags.  In order for this to work as a fault tolerant configuration, each server must have a connection to each of the in-rack switches.  On our normal, non-virtualized linux server deployments we have been using standard link aggregation (otherwise known as bonding or NIC teaming) with LACP (Link Aggregation Control Protocol).

According to the documentation, XenServer, which is really just Linux under the hood, supports network bonding, so this should be the same, right?


Rather than using LACP, XenServer actually uses something called "Source Level Balancing," which is based on the standard Linux "Adaptive Load Balancing" method of bonding (See Citrix's KB article CTX124421).  The really cool part of this bonding mode is that it requires no knowledge on the switch side of the connection to make it work.  Instead, the hypervisor migrates VM network traffic from port to port by sending a "gratuitous ARP" through the new port with the MAC address of the VM to be moved.  In an active-active configuration, XenServer monitors the traffic for each of the running VMs, and will rebalance as needed every few seconds (according to the manual, 10 seconds).

So, don't do what I did and configure the switch ports that XenServer uses as LAG groups.  Otherwise you'll end up with a bonding mismatch and waste time trying to figure out why you are having weird networking issues.