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Help in Plex media server

Posted: Wed Mar 04, 2020 4:31 pm
by Uhlmann
Hey guys,

I am building a Media server, which will be primarily used as a Plex server and transcoding hub (Both live transcoding and trancoding the media library). There are some alternate uses, but performance is not integral to the proces for these tasks. This might be a bit overkill, but the server will be hosting roughly 6-10 concurrent users, and consumes a lot of data as the various users will skip between movies, shows, music etc. This is also one of my questions in terms of PrimoCache, I will most like be using this as read Only Cache, as write operations in my Raid setup will be mostly maxed anyway. But I am unable to verify how often Primocache will swap data into the L1+L2 Cache, because as far as I understand it waits for idle operations. Does this mean that it will not load full movies into the cache before the system idles? This might just be my limited understanding, but an essential part of my caching scenario is that data is dumped into the cache, so buffering and fast forward or searching operations are performed quickly, same thing goes for trancoding a 40GB file into a 2GB file.

The system will be set up as:
CPU: Ryzen 5 3700x
GFX: Nvidia Quadro P400
Memory: 32GB DDR4 Memory
Boot Drive: 256GB NVME SSD
Storage: 8 x 10TB HDD 7.200 RPM in Raid 5 (63TB of usable space, 24TB occupied)
L2 Cache: NVME, Size ????

First off: I would really like a recommendation on L2 Cache size, I have a really hard time figuring out whether a large cache will benefit me. Media files can be up to 10gb in size, and I want to utilize the L1+L2 cache for speeding up buffering and in-video skipping, as this can be extremely slow on regular HDD. In terms of budget Anything from 256GB-1TB is in my budget range, but I would prefer saving the 3x cost of 1 TB if it will not yield any gains.

Additionally, I have 32 GB of memory, but will not use more than 16 GB, will 16GB L1 cache be sufficient.

Lastly: Any guidance on block sizes or special tricks for a setup like this would be appreciated.

Re: Help in Plex media server

Posted: Thu Mar 05, 2020 2:45 pm
by support
Uhlmann wrote:
Wed Mar 04, 2020 4:31 pm
But I am unable to verify how often Primocache will swap data into the L1+L2 Cache, because as far as I understand it waits for idle operations. Does this mean that it will not load full movies into the cache before the system idles?
L1 is immediate while L2 is on idle. You may tune L2 gather speed to "FASTEST".
So far PrimoCache populates data into cache (L1/L2) when data is read. It does not support pre-load full movies. In future we may support read-ahead feature.

I'm wondering if PrimoCache will help a lot in your scenario if your users consume various data while hot data is not much. L2 cache size is also depends on the amount of hot data. If the amount of hot-data is big while the cache space is small, old saved cache contents might be replaced very often, causing bad cache effects and efficiency. Of course, if your hot-data is not much, you may not need to use big cache space otherwise it might be a waste of your investment.

Re: Help in Plex media server

Posted: Thu Mar 05, 2020 7:34 pm
by Jaga
I found that with large files and a lot of turnover (frequently loading different large files), the cache was FAR better to place on the C: volume (where the Plex database and loose-leaf files like thumbs) were held. Caching the Plex media volume itself gave very low hitrates, since I was constantly watching different large media files.

My advice would be to home media on a volume that isn't C: (normally you wouldn't anyway) like D: or E:, and then have all Plex files residing on C: fully cached. Since you are caching less, you can enable write caching if you want to. It will help Plex with it's updates, and nightly cleanup routine.

Re: Help in Plex media server

Posted: Sun Mar 08, 2020 9:03 pm
by Uhlmann
Thanks guys, this cleared up a lot of things for me, thanks!