New estimates of the alert stream sizing have been developed. Jeff Kantor feels that LDM-151, which already has an estimate of the total alert data size per night, is an appropriate place to record the updated values. The edited text is available at https://github.com/lsst/LDM-151/pull/56 for now, soon to be merged to master and then uploaded to DocuShare. (I'm holding off a bit in case there are other LDM-151 updates that could be batched with this.)
Some of the expansion (from 600 to 800 GB/night) comes from changes to the DPDD, especially the 12 months of history, including non-detections, and larger postage stamps (up to 50x50). The variable part of the expansion (from 800 to 1200 GB/night) comes from potential Avro overhead. While I wasn't able to generate a complete alert packet in the short time I've devoted to this, I came up with up to 50% overhead based on figures that Maria had provided and a few small test cases. It is possible that we may find a way to shrink this, but it will be quite difficult to reduce it below the 800 GB figure.