I need to alter a column in a table with 8 million records. I need to make it c(10) from c(7). Here are my questions:

1. Should I use varchar? Most (80-90%) entries are c(7) with the rest being up to c(10).

2. How does SQL Server handle the change internally? Create new table and copy data? Create new column, move data, delete old column, etc.?

3. What is the most efficient way to make the change without bringing the system to it's knees?

TIA

John