It’s literally the same path I walked when Ryzen launched, so I have direct experience/notes, the power costs have changed drastically, so smaller differences give bigger savings now which makes it even more worthwhile. Your main savings will be in two simple areas, storage and transcoding. The price capped rate for electricity nationally is 28p (round nunber), it’s likely to go up by 1/3 later this year, that means each watt of power costs £2.45/yr now, or likely £3.27/yr by December, so, with that in mind, let’s cover the obvious: You have two main areas you can save power in, storage and CPU (transcoding).
If we start with storage, you know 2TB drives are way too small, just running one 24/7 idle is costing you £12.25-17.15 per drive, you have 10 of them... by the end of the year you're looking at £16.35-22.89 per drive... times 10. It's £230-40ish for a brand new 10TB Iron Wolf or EXOS Enterprise drive or £220 if you shuck them, if we assume that replaces 5 x 2TB drives, you're saving £91.56/yr even allowing for the cost to run the new drive, clearly that makes sense over 3 years and they're warranted.
In terms of storage strategy, rather than RAIDZ2 as you don't seem to need the IOPS, have you considered something like UnRAID? It's discounted till the end of the month and will allow you to pool random sized drives while keeping dual parity if you want. The other advantage is you can spin down the pool, if a client accesses a file, it only spins up the drive it's on to read it. The other benefit of this is you'll obviously have other dockers running, they can sit on a cache drive (say a reasonable size NVMe) and just move data over to the array periodically. The only drives that are spun up during write are the parity drive and the drive being written to.
Next up is transcoding. Lets agree that software transcoding as you are now is both inefficient and power hungry. Plex themselves admit the numbers below are not that accurate, but they are what they are, so we'll use them.
- 4K HDR (50Mbps, 10-bit HEVC) file: 17000 PassMarkscore (being transcoded to 10Mbps 1080p)
- 4K SDR (40Mbps, 8-bit HEVC) file: 12000 PassMarkscore (being transcoded to 10Mbps 1080p)
- 1080p (10Mbps, H.264) file: 2000 PassMark score
- 720p (4Mbps, H.264) file: 1500 PassMark score
Source:
https://support.plex.tv/articles/201774043-what-kind-of-cpu-do-i-need-for-my-server/
So what you have (2630L v3) has 7K ish of CPU Mark and according to Plex is therefore capable of 3+ 1080p H264 transcodes (due to the way transcoding works, it’ll be more, but just go with it). To do 3, your CPU usage will be high, fans spinning up, power usage spiking and you have no hope of doing 4K HEVC, let alone 10bit HEVC. As I type this I have a tab open showing a Plex server doing an HEVC 10bit transcode to SD (don’t ask) and another 1080p H264 to 720p H264, the system usage is under 5% and Plex is only taking 2% of that. Hardware transcoding will literally change the way you view transcoding, and unless you are the kind of person who sits with a magnifying glass working out what gives the least edge diffusion in dark scenes or fast motion, you won't be able to notice the difference between a software transcode and a hardware transcode. To do this in Plex, you need an intel CPU with iGPU, ideally 8th gen or newer (HD630) or an Nvidia GPU with NVEnc capabilities - the consumer range is limited to 3 concurrent transcodes, you can either patch the driver or buy a Quadro which isn't limited - GPU RAM will limit your maximum number of transcodes). Generally aim for a Quadro P series or newer, Nvidia will claim Maxwell can't do HEVC, but the M2000 is a 2nd gen Maxwell (like the 960) and can. A GPU will add about 11w idle from memory and it's not loading the GPU up like gaming or mining, the NVEnc hardware is separate. The P600/620 are reasonably inexpensive (£60-70 used), the P1000 is likely a better bet (85-110 used) and the P2000 tends to be silly money - they just don't make sense compared to iGPU unless it's something like Ryzen or a Xeon w/o iGPU.
As you're looking to reduce power, the technically best option is a modern 8th gen CPU w/iGPU, it literally can't be beaten at this stage in terms of efficiency. I grabbed an i3-8100 and MATX ASROCK board for all of £40 earlier this year, I had planned on swapping the i3 out for the i5 8400 I have as 4c to 6c with a higher clock rate sounds like a worthwhile jump, as you say, same iGPU, same transcoding performance. Reality is I put that little i3 into service on the 22nd of March this year, it's never felt limited or been a bottleneck and I work my servers HARD. The i5 is literally sat doing nothing, and I have been in adding and upgrading hardware at several points, but it's just not been something I felt I have needed to do. My i3 NUC on the other hand (2c) did feel like a compromise by comparison, in all honesty i'd happily have an 8100 again, but if the money is right the 8400 is going to be more capable.
The elephant(s) in the room here are as follows:
1) GSuite Business is £15/m ish and gives unlimited* storage when using team drives and mounting them via rclone (*technically each team drive is limited to 400,000 files/folders), you also need a domain and you are limited by your internet connection (especially upload).
2) Moving your services to a VPS or dedicated server with symmetrical gigabit or faster can actually be cheaper than powering hardware locally, combine this with 1) and your perspective on the world and how storage can be managed changes quite quickly.
You’d think that was a good idea as a Plex server, I mean the M1 is a revelation of performance and efficiency… it turns out it’s really, really not (I say this as a man with two mini’s and an obscene number of iOS devices in the household, so I really wish I could recommend the mini). It’s just not well enough supported at this stage to do the job reliably and without issue. If you want efficient, a Dell OptiPlex 3060 or HP 290 G2 etc. is £100+ and a much, much better choice.
(Didnt measure power draw here either... But its not going to be excessive given the lower TDP chip).