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How big to make a SSD dedicated to Docker appdata and VMs?

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I'm setting up my first UnRaid server this weekend. I have a 256GB SATA SSD (Samsung 840 Pro 256GB) that i'm planning to use dedicated to cache for the array (mover will only move stuff off this SSD).


I want to get another SSD (maybe NVME) dedicated for docker app data and running VMs because I heard that it will keep docker/VM performance stable when a ton of write/read is happening from the cache SSD; but not sure how big to make it. I know stuff like Plex/Jellyfin metadata can get pretty big but I'm only planning on having like 1TB of TV/Movies at most in my array for Jellyfin, so i don't imagine the dockers needing *too* much space.


The VMs on the other hand i have no clue how to spec out. If i want my VMs to run on the a dedicated NVME drive does that mean all the data they access needs to be on it? Or, rather, would it be a good idea to do this? For instance if I want a VM to play games on Dolphin do i need to store all my ROMs/ISOs for Dolphin on the NVME drive or should I just have the VM access the array for the ROMs/VMs?


If i have the VM access the array for the game ROMs/ISOs i feel like i'm not getting any performance enhancement since it's going to be reading off the array instead of the NVME, or is the performance of reading the ISO not really the limiting factor here.


Basically when people say the run their VMs/Dockers off a dedicated SSD, what exactly is being stored there besides the docker images and the VM images?

Edited by Taako
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I have an 860 pro 1 Tb.   2 always on windows 10 VMs with numerous pass through devices.  1 workstation and 1 Steam stream for all gaming.  I also have 1 always on docker.   In addition to this I have 2 VM and 2 dockers that are turned on as needed. 

I have zero issue with stability or speed. 

This is all on a single cache drive. 

Seperatly I store all the games on a user share in the array.  This share is mounted within the VM.  Unraid lets vms access shares within the server, not across the network. Games load at the speed of the mechanical hard drive.  

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I have 2x500GB SSD btrfs raid1 cache pool for caching user share writes and post-processing downloads, and 1x256GB XFS "fast" pool for dockers / VMs and anything else I want to keep on fast storage, such as a copy of some music and photos for other devices on my network to access for wallpaper, music apps, etc.


Both of these pools are way overkill for my actual usage patterns but I had some leftover hardware from other builds.


For a long time I ran with only one pool, 2x275GB SSD btrfs raid1 cache pool, and it was more than enough for caching and everything else, but I only have a single Ubuntu VM for playing around in. If you were running multiple Windows VMs I can imagine wanting more.

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