SQL Server NTFS allocation unit size On Windows 2008 R2 running SQL Server 2008 R2 how imporatant is the NTFS allocation unit size on DISK IO performance. It appears to me that server admin who built the few servers for a mission critical app left NTFS allocation unit size (cluster size) to default 4 KB instead of 64 KB. SQL server is already installed. 

Does it worth to take pain -- to uninstall SQL -- format the drive with 64 KB cluster size and reinstall SQL server?
You shouldn't need to uninstall/install: your data and log files should be on separate disk arrays/SAN Luns from the binaries.

Saying that, 64k NFTS cluster is highly recommended all over the place.
SQL Server does IO in extents which is 8x8k pages = 64k, basically.

For actual numbers on performance differences, I can only find this http://tk.azurewebsites.net/2012/08/ (Azure, but still SQL Server)