I contend that it never mattered. Mine are all HR20's. None have ever experienced a slowdown due to the drive being full, and the drives have been full often, including since 2007. I have, in the past, often let the drive fill up and never deleted a thing, allowing the "Until Drive is Full" algorithm to handle it. I have one at 7% currently, and it is just as fast as ever. Since there is no technical reason why data on a HDD that is not being accessed at the moment would have any affect on the data that is being accessed at the moment, I'm going to have to go out on a limb here and say that the idea of a HDD or DVR slowing down just because the HDD is full, is probably nothing more than superstition. You may have cause and effect, but they are not related, they are simply coincidental. Its a jump to an unproven conclusion. Human nature at work. For me to lend any credibility to the theory, I would have to have the actual mechanism of such a phantom slowdown explained to me. Go for it. I'm always eager to learn something new. PCs? Well, that's different. PCs fragment files, DVRs don't. More indexing? Doubtful; that is based on what is in the guide, not what is on the HDD. Larger DB? I don't think so, because even the catalog DB of a 2 TB drive is pretty small and quickly read. My Macs have some 100,000 files and lord knows how many extents B-tree file fragments on the HDD, and that is not slowing things down, from all appearances. The 1000 or so files you might be able to shoehorn into a DVR's 2 TB drive would hardly make a dent, DB-wise. If your DVR is slow, point to the usual suspects, and a full HDD isn't one of them. DVRs with empty HDDs also have no or few SLs scheduled. There is one thing that can make a DVR with an empty HDD seem faster, but it is not because the HDD is empty, it is simply coincidental with the fact that there are also no or few SLs on it. SLs can slow down DVRs because any new recording request has to be vetted against all of the other ones that have standing reservations, serially, one at a time. Delete all of your SLs and leave your HDD full, and your DVR will be peppier the next time you schedule a recording (all else held equal), especially a repeating recording. There is a method to the madness of limiting the SLs to 50, in that it prevents a slower UI, which gets exponentially slower with the number of SLs.