As StuartS comments - almost any drive will work in a RAID environment; it just needs to be compatible with the chosen controller; and the drives involved of the same size. If they differ in size then the default size/capacity for each drive involved will be that of the smallest drive installed. Quite what the store people really meant to say - who knows… Possibly they were a little confused as to how RAID systems work?
This link explains the whole RAID system in a very clear and simple graphic style…
Raid 1 (Mirror) is the minimum I'd go for. Many NAS systems targeted at the domestic and small office environments are two drive systems in a mirror. Having one for a few years now, and recently lost a drive - it was a relief to have the RAID 1 arrangement as it meant I could still use the remaining drive whilst waiting for the replacement drive. And the automatic rebuild of the mirror was quite easy and fast. No data lost.. One thing though.. Even a server (whichever RAID it is) needs a backup. So I have a USB drive across mine to make backups at intervals… Then if for whatever reason both drives went down. I have the backup around
If a server is to be on for lengthy periods - say most of 24x7x365… excluding holidays… Then wise to install the heavier duty drives; rather than those typically installed in just about every desktop etc… Those are designed for some reasonable down time and relatively short times up… Heavy duty drives sometimes cost a wee bit extra - but you get what you pay for; increased reliability not the least.
message edited by trvlr