In the Rackspace overview for their next gen servers they have a table of flavor options.

In the table there is a column called RXTX factor with no explanation. I tried googling, but couldn't find anything definitive (something to do with receiving and transmitting?). It looks like it goes up with the bigger servers, so I'm guessing the higher the better. Could someone enlighten me?

  • 3
    Contact their sales/support department to find out. – Sven Jan 6 '15 at 9:43
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    You'll find more if you don't search Rackspace specific. This is a OpenStack term. E.g. see here for some explanation: markmail.org/message/… – faker Jan 6 '15 at 10:28
  • @Sven great suggestion.. have done so (see my answer) – Arth Jan 6 '15 at 10:41
  • @faker Thanks for the link.. that makes more sense, but weird that that google only finds an explanation found hidden in a forum discussion. – Arth Jan 6 '15 at 10:43

After contacting support, this is the answer they gave:

RXTX Factor

Aggregate outbound bandwidth, in megabits per second, across all attached network interfaces (PublicNet, ServiceNet, and Cloud Networks). Outbound public Internet bandwidth can be up to 40% of the aggregate limit. Host networking is redundant, and bandwidth is delivered over two separate bonded interfaces, each able to carry 50% of the aggregate limit. We recommend using multiple Layer 4 connections to maximize throughput. Inbound traffic is not limited.

Picking an example: first row 512MB standard instance, RXTX factor 80.00/mbs is the maximum speed across all the network interfaces (public, private, cloud network) that data can leave the server

The first paragraph of this can be found in their docs

This seems like a bit of a twisting of what RXTX factor intuitively should mean and is not a ratio but actually in Mb/s.

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    Would've been simpler if they referred to it as 'aggregate outbound bandwidth'. – AStopher Jan 6 '15 at 20:10

It's far from clear but I'm reasonably certain that it's the ratio of how much bandwidth there is available for both receiving and transmitting. For instance a machine with no limitations would have a RXTX factor of 100, whereas a machine that could only receive half of what it could transmit would be 200. Basically it's just rate-limiting on the network and their quite-hard-to-follow arse/ass-covering weasel-wording :)

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    I would have thought that too, but according to support (see my answer) it's actually a Mb/s value on outbound bandwidth. Thanks anyway! – Arth Jan 6 '15 at 10:39

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