simeondorelov

Hey fellow unraiders, I'm new to unraid and in need of a bit of guidance on how cache disks work in unraid and how best to utilize them. Setup: UNRAID - Version: 6.9.2 Array - 3 identical HDDs one of which parity, 1 SSD as cache disk. Expectations: I want to run docker containers and VMs off of the SSD to ensure better performance. My expectation was that cached shares would prefer to read and write from the cache and periodically copy data back to the main array to ensure it is on safe storage. Observed: From reading the unraid documentation it seems that data is actually moved off of the cache instead of copied and this is only done if the files in question are not "hot". It is also not clear if the cache affects read performance. Now, given that the shares are storing container / VM data, a lot of which will be constantly seeing I/O I am worried that a) that data will never leave the cache and b) even if it ever does that would have a certain impact on performance. So is the unraid cache only used to cache writes or as a general purpose cache? If some data is comitted to the array can it be "upgraded" back to the cache when it becomes "hot" again? Can the cache copy instead of move data? Am I better off just adding my SSD directly to the array so that it is parity protected and forcing relevant shares to use the SSD drive exclusively? (this is somewhat inconvenient since you can't make more general use of the cache for all shares) Are there other possible configurations here I am not seeing? Thanks in advance for the help! -Simeon