What size are the biggest SQL Server database installations in the world?
Look these old numbers:
- 2005 TopTen Award Winners - PDF
More recently, check this out: Microsoft Applauds 1.1 Petabytes SQL Server 2008 Database
Since the other answers are outdated / broken references.
Here is an answer from 2014:
Uncompressed, the Options and Equity archive measures 2 petabytes (PB). With page compression, it measures 1.5 PB.
They also claim that on each year they add 500TB to the database.
See: NASDAQ OMX Group Case Study