My advice is to put the ownCloud /config on an SSD cache share. Just putting the /data on disk 1 probably won't accomplish what you want depending on the activity on ownCloud. Any /data file activity would spin up the disk. i.e. uploading, downloading, or viewing files.
Put the ownCloud /config on a SSD cache, and back it up regularly to the array. ownCloud has a plugin in the marketplace that does a database backup regularly, and you can safely copy the /data folder to the array with a User Script, even with ownCloud running. You will also find that ownCloud will be more responsive on a SSD share.