'Staff' can mean several things and the rules of 'staffs', 'staff', or 'staves' for plural varies with each:
- staff: the stick a wizard carries in fantasy novels. Plural is 'staffs', though the odd occasion you'll see 'staves'.
- staff: a piece of stick. Plural is 'staves'. For instance a wooden barrel is composed of staves.
- staff: a musical notation. Plural is staves.
- staff: the people of an organization. It's possible for plural to be 'staff' OR 'staffs'. Eg. Microsoft has a staff of 1000 in technology and a staff of 2000 in marketing. You could say, "The staffs/staff in technology and marketing include 3000 people".
'staff' in this people sense can take 'is' or 'are'.
eg. "All the staff ARE present today" and "All the staff IS present today". Which version is most common will vary on the country.