Spanning drives (performance and integrity)

for my plex server (data is store in a DAS external drive enclosure) I need to add an additional drive and was wondering if I span this new drive with an existing is there any performance degregation? when I say span the drive I just mean through Windows Drive Utility not in any raid format. Just so 2 drives appear as a single volume for ease of use iun this senario. Also does this increase my chances of losing data? i.e if one drive fails will I potentially loose datas from both drives? or is the data seperate and just read as a single volume (if that makes sense)

Sounds like a raid0 kind of setup. If it is anything like this, it increases read and write performance, it is very susceptibe to catastrophic failure if one drive even has a problem.