performance - One or many databases for application for many clients in PHP -

i writing php application in zf. customers use sell products final customers. customers host application on server or use own. of them host application on server.

i design 1 database customers @ once, every customer use same database, of course products etc. assigned particular customer. trivial.

i use separate database every customer, database structure simpler. use separate subdomains , maybe file location, detail.

which solution have better performance , how big difference? 1 choose?

i use separate database each customer. makes backup , scaling easier. if ever large customer needs custom changes schema, can easily.

if 1 customer needs restore data, single database trivial. on shared db, harder.

and if large customer ever gets lot of traffic, can put them on server minimal changes.

if 1 site gets compromised, don't have of teh data in 1 place, damage mitigated site hacked.

i'd recommend going 1 db per customer if possible.