Size of mailboxes on Microsoft Exchange 2003

I am currently administering a MS Exchage 2003 server. We are at the default db size of 18gig and the mailboxes sizes in total is approaching that limit. I have two options 1)increase the db size to keep letting the mailboxes grow. Hard drive space at this point is not a problem or option 2) archive mailboxes. I don’t like option 2 because .pst files get corrupted and copying emails to a microsoft folder as a .msg file appears to create search problems. If I allow mailboxes to grow by increasing the default exchange db size will the exchange db get slower and can a large mailbox fail?

Thanks in advance for all responses.