I noted that COLDSTORE was mentioned in this discussion (disclosure: I represent Veracity, the manufacturer of COLDSTORE).
John is correct - COLDSTORE is an option for this kind of application. It is ideal for video retention times of 30days or more, and the longer the retention, the more suited it becomes. Before John (rightly) admonishes me for making this a sales pitch, I did have a technical point (well, two actually) :
COLDSTORE can exploit the latest 8TB SMR disk drives, which are incredibly low cost per TB and means that the end user can get very high capacity cost-effectively. "SMR" stands for shingled magnetic recording and means that the writing tracks are partially overlapped to get higher density on the disk. This is ideal for archive purposes where you are not going to change the data. It is totally unsuited for normal database or IT style use and cannot be used in a RAID5 or 6 system. However, the SFS or sequential filing system within COLDSTORE writes the whole disk sequentially (and optimally) and then makes no further changes to it until the retention time is reached and the disk is overwritten with new data. This means that these very high capacity SMR drives are perfect for COLDSTORE and thereby for long-retention video surveillance applications.
COLDSTORE is regulary used in applications requiring 90, 120 days file retention, and we have done a number of projects with 6 months and even 2 years' file retention. These are typically multi-petabyte projects.
I would also agree with John that the key to reducing the storage requirement for Ken Jenkins' project is to carefully choose the right IP camera. Choosing one with even slightly better compression efficiency makes a big difference when the retention times are long. However, also look at the storage solution - some solutions have a far lower total cost of ownership than others, so take into account capital cost, disk costs, power consumption over the expected lifetime, cooling equipment costs, cooling equipment running costs and last but not least, UPS equipment costs. The more power consumed by the storage system the more expensive all of these will be.
Sorry, did I mention that COLDSTORE uses 60W for 120TB of storage ? Half a watt per terabyte is good news for the TCO calculations mentioned above. (That was my second technical point).
I hope this is helpful.