Replication and compression

[Chicken76]

Not new to FreeNAS, but new to replication. My question is: if the source and destination datasets are both lz4 compressed, is it necessary/advised to use stream compression?

I read somewhere that newer versions of ZFS are capable of sending the snapshots as they are on disk (compressed) and avoid decompressing the source, sending (maybe adding compression to the stream) and then decompressing at destination only to re-compress in order to store on disk.

 

[MatthewSteinhoff]

if the source and destination datasets are both lz4 compressed, is it necessary/advised to use stream compression?

TL;DR: {shrug} Try it both ways.

We've tried it both ways and didn't see a difference in performance over either a 1G or 10G connection. So, over a LAN, it doesn't matter with our data set.

We have three remote FreeNAS units that replicate to the mothership over VPN connections at between 5mbps and 20 mbps. Again, we don't see a difference in performance over the VPN. The bulk of our replicated data is PDFs and JPEGs which are already compressed and the rest of the data - typical Microsoft Office documents - are such a small component that compression doesn't make that much difference. Plus the VPN does compression which may or not be be a factor.

If your CPU sweats when you're replicating, maybe turn stream compression off. If you network sweats when you're replicating, maybe turn on stream replication. Really though, we don't think it makes enough difference to matter either way.

Cheers,
Matt