I wouldn’t call it negligible, but I don’t think you would see the full benefit with a media server.
I would probably expect the same amount of life out of a 7200rpm drive as a 5400rpm. 7200rpm runs faster (obviously) and hotter, so with longevity I think they might be even.
I have two 256GB WD Black NVMe Drives (2017 model) in a RAID 0 read cache… Haven’t noticed a difference.
If anything, I’ve justified it in my head as helping offload some of the work from the HDDs. Plex is constantly reading files for the server, so if those files are getting moved to the read cache then it’s less movement for the read heads on the HDDs.
If you want to experiment, start with just one SSD. The Synology supports NVMe so it’s up to you if you want that, or a standard SATA M.2 SSD. (I’d recommend the new WD Blue NVMe drive over the WD Black [but if you get the Black, get the one w/out a heatsink; not sure if the heatsink will fit])
Let’s be real, it can only be used as a read or read/write cache, so there’s no sense in buying a faster (and more expensive) Samsung or WD black NVMe.
…both large sequential read or write operations (e.g., HD video streaming) and entirely random data reading patterns lack re-reading patterns, and thus will not benefit significantly from SSD caching.
I’ve a DS414 with 3 x HGST 4TB Deskstar NAS drives and 1 x HGST 4TB Ultrastar drive. I don’t remember exactly when I purchased the drives, but the Deskstar drives went out of warranty in 2015 and the Ultrastar (5 yr) in 2018. They’ve never given me any trouble and are incredibly quiet. The NAS sits ~3’ from my desk and I never hear them.
The DS918+ has 3 x HGST 10TB Deskstar NAS drives and 1 x 12TB Seagate 12TB Ironwolf drive. The HGST drives were purchased in Nov 2017 and have never given me any trouble. They are, however, not nearly as quiet as the 4TB drives in the DS414. I won’t call it unbearable, and not nearly a Hoover, but you definitely hear the read/write activity. I was definitely disappointed when I fired up the NAS and heard the drive noise. I was expecting them to be as quiet as the 4TB drives. If I hadn’t caught an incredibly good Black Friday price I probably would have returned them. The 12TB Seagate has been in service for about 9 months and has given me zero problems.
I wouldn’t worry about 5400 rpm vs 7200 rpm. The 6 TB Red drives have a transfer rate of 180 MB/sec (PDF data sheet). Gigabit Ethernet has a theoretical maximum of 125 MB/sec (I get 115 MB/sec transfers between my PC & 918+). The highest bit-rate movie I have is 4K HDR rip at 80 Mbps (i.e. 10 MB/sec). You’ll be able to stream multiple high bit rate movies w/o having to worry about disk throughput problems.
as helping offload some of the work from the HDDs. Plex is constantly reading files for the server, so if those files are getting moved to the read cache then it’s less movement for the read heads on the HDDs.