I just built an unraid server last night, 3 1TB HDs, 1 parity.  I'm using unraid to store files 2-10TB in size, will a 500GB nvme drive configured as a cache drive help with write performance? From what I've read the cache drive seems to be a file cache, not a block level cache. I've been looking for a description of how the cache drive works under the hood, but havent found any resources yet.

 

Thanks.

25 minutes ago, segway said:

files 2-10TB in size

Do you mean GB?

6 minutes ago, trurl said:

Do you mean GB?

Yes, my bad, most files are 2-10GB in size.

I'll install the nvme, my only concern is as I'm initially writing files to unraid, if the cache fills up before mover moves files to the array, I understand the writes will fail. I'll have to look at mover options I suppose.

For your initial transfer of data to your array, you will want to:

• Disable your writes to cache (Primary Storage to array, Secondary Storage to None) for each share you are copying to
• In Disk Settings, set Tunable (md_write_method) to Reconstruct Write

Once you've copied everything over, you can set them to what you wish.

 

Cache will not save you any time if you overflow it, and cause you problems during large transfers.  As it will take as long as it takes to write to the array - cache just delays the pain, making it faster in the long term, but then you do the write again later (when you are less concerned about speed). 

 

For the Reconstruct write, that does make the transfer faster.

 

 

Thanks for all the replies, so far my initial copies havent filled up the cache drive before they're moved off to the array.