After much benchmarking to choose the best filesystem and configuration for OMV to be a backup target for vRanger backups (large files), I chose XFS as the filesystem and serving it up with SMB. My existing vRanger server was backing up to a a different device (DataDomain 510) and was providing good performance, so I know the vRanger server is configured acceptably.
Having switched the backups to my OMV implementation, I was very disappointed to see abysmal performance, but I'm not sure why. I see my top process(es) is smbd. Here are a couple of the charts (since a picture is worth a thousand words), hoping someone might be able to offer some suggestions to make the OMV a viable alternative: