Use SSDs as both "copy here first" and archive

[Colin Yates]

(I am sure I saw the answer to this but I can't find it, so apologies if this is answered already)

Hi there,

I have a pool with 4x2TB spinning disks and 2x1TB SSDs, with about 3TB free. The pool is only for large (legal!) media files and is now pretty much read-only. Should there be any new writes I would like them to land on the SSDs first but I _don't_ want the SSDs to be completely evacuated. Instead, I want to keep a certain % of the SSDs free, but the rest of the space should be considered fine for long term file storage.

Using the SSD plugin gives me the "write first to SSD" but it then tries to completely clear the SSDs.

To put it another way, I want all disks used for file storage, but I want to keep X% of the SSDs free as a write cache.

Is this possible ATM?

Thanks!

[Umfriend]

I don't use the SSD Optimizer, I am not sure. I think you can't do this through a setting. What might work though is if you repartition the SSDs, use one partition for storage and the other for cache. There are some caveats to this as well though

[Colin Yates]

That's not a bad idea. I guess I could also have 1 SSD for incoming and the other marked as archive as well...

[Umfriend]

The downside is, I think, that DP by default fills (archive) drives that have most space free first. In your case, as the SSD is 1TB, DP would write to the spinners with 2TB free first.

You can adjust this with some balancers and if you know which files you want to be prioritised to be stored on the (archive) SSD then you could use File Placement Rules.

[Christopher (Drashna)]

Yeah, there isn't a good way to do this with the SSD Optimizer, though, you can use the File Placement Rules to lock some folders to the SSDs.  That may be "close enough" to what you want. 

[thewinger]

I was trying to do something similar. Using an SSD as balancer and storage for VM folder (for performance).
But a question came to my mind. If I add a file placement rule to have the VM folder always in the SSD... what happens if I also activate folder duplication for it?