Unraid read speed and cache

[MichaelBernasconi]

Hi everyone,

 

I have an Unraid server on which I'm running a bunch of VMs. My array consists of 2 of HDDs (no parity yet) and I have a fast SSD around that I'm currently not using. I ran passmark on a Windows 10 VM and got a result that I do not understand. According to the results my disk performance is in the 99th percentile. How can this be? My 2 HDDs should not be fast at all, right?

Now on to my question about cache. My idea was to have files that I want to access fast on the SSD (cache) and also on the array (for backup). That would mean that the VMs only ever interact with the SSD and the mover writes back the updates to the array when it has time. As far as I can see Unraid does not really have that option. Both the "prefer" and "only" mode would result in the data being stored on the cache drive only while the "yes" and "no" modes would result in the data only being stored on the array only, right?

Did I get something completely wrong here? 

 

Best,

Michael

[itimpi]

No you got it right - files can only exist in one place.

 

For apps where performance matters the normal solution is to have the files reside on the cache and then have something in place to make backups to the array.    The CA backup plugin helps with this.

 

 

[MichaelBernasconi]

Thank you very much for the quick reply! Having the data only on the cache drive and then making a backup from time to time seems like a reasonable idea. Do you have any idea how I managed to get such good disk performance in passmark? The VM I tested on is only 20GB and completely fits in RAM. Could it be that Unraid somehow moves the whole VM into RAM?