Cache Pool Best Practices

[SNDS]

Hey folks,

While I am waiting on my build parts to arrive in order to start tinkering with Unraid, I did some searching on the forums here with mixed results so I wanted to see if the community would be willing to give me some perspective and insight on the cache pool before I get rolling. 
 

1. Is there a limit on how many drives can be in a cache pool?
2. Is there a best practice for the size of a drive? I am using this machine as a Plex server/media sourcer (newsgroups mainly), if that helps.
3. What's the word on NVMe cache pools? Is it any better to use the faster I/O on those devices for my use case (see #2) even if it will over-saturate the array when migrating files?

 

I haven't purchased the cache drives yet because I'm unsure about the above and it will guide my purchase there.

 

Thanks folks!

[trurl]

There are many ways to answer your questions and different people will have different uses.

 

Do you have a good idea of the ways in which people typically use cache?

 

How do you intend to use cache?

[jpowell8672]

1. Up to 24 devices in the cache pool

2. Depends on amount of data you will be grabbing and how often you want the mover to transfer the data to the array. I would go for a minimum of 256gb ssd. I use 2 1tb m.2 drives in btrfs raid 0 for high I/O and speed but you could do a mirror for protection or just go with one single drive with no loss protection.

3. NVMe is absolutely better but not needed if you don't need the higher I/O and speed.

[SNDS]

I don't know how others use the cache specifically. But I know, that for my sake, I want to be able to use newsgroups (apps like Sonarr/Radarr/Lidarr/SABnzbd)  and I know they can take a toll on the random read/write of drives when using them conventionally, so I suspect it may be good to have a good cache for writing files coming from newsgroup sources as they could be large and one doesn't want to hammer the actual array until it's time to offload. I could see files up to 25-30gb downloading up to 5-8 files at any given time during much of the day/evening depending on the requests and needs. I'm also considering a LANCache but that won't be a constant download, most likely I'll download a bunch of stuff up front then the LANcache will be refreshed after I have a LAN event at the house.

 

--edit--

Supplemental context: the main use cases for my server are in order of priority - Plex/Newsgroups Downloads/LANCache/Game Servers

Edited September 24, 2019 by SNDS

[SNDS]

*BUMP* Anyone have thoughts on the drive size and pool size? I'm thinking of going @jpowell8672's route and use dual 1TB NVMe drives in Raid 0 for newsgroup services and LANCache use cases.

 

As an aside, what's the max that one can do for parity drives? I was thinking of getting 2 4TB 7200RPM drives for parity.

[trurl]

13 hours ago, SNDS said:

use dual 1TB NVMe drives in Raid 0

Are you sure you don't mean raid1?

[jpowell8672]

5 hours ago, trurl said:

Are you sure you don't mean raid1?

Im running 2 Samsung m.2 nvme 970 pro 1tb in raid 0 for the speed and I/O because these are premium quality m.2's which are less likely to fail. Yes I know any can fail at any time but I regularly backup to my array so if 1 or both died I would be fine and not need the raid 1. I get the faster speed, I/O & 2tb of space.

[SNDS]

3 hours ago, jpowell8672 said:

Im running 2 Samsung m.2 nvme 970 pro 1tb in raid 0 for the speed and I/O because these are premium quality m.2's which are less likely to fail. Yes I know any can fail at any time but I regularly backup to my array so if 1 or both died I would be fine and not need the raid 1. I get the faster speed, I/O & 2tb of space.

This.