Jonathan,

http://download.microsoft.com/download/4/7/a/47a548b9-249e-484c-abd7-29f31282b04d/SQLIOBasicsCh2.doc

A SQL Server database can be restored or attached on a system that has a smaller sector size. To help guarantee data integrity, the larger sector size should be evenly divisible by the smaller sector size. For example a 4 KB source restored/attached to a 1 KB or 512-byte destination is an evenly divisible size. Restoring or attaching to a smaller sector size such as 1536 bytes does not fill the “evenly divisible” requirement and immediately requires sector rewrite operations to occur.

SQL Server is not designed to dynamically upgrade the database to the larger sector sizes. SQL Server disallows restoring or attaching a database on a system with a larger sector size; it generates an error message and prevents the restore or attach operation. Enabling a database to function by using a smaller formatted sector size than the actual sector size violates the WAL protocol because the sector size variation guarantees the log records will not be correctly aligned with the physical sector size and log records will be rewritten.

At the time of publication, some current subsystems report sector sizes larger than 512 bytes but most do not. The larger sector sizes involve newer technology and require API changes at the operating system level. Future changes in Microsoft® Windows and SQL Server will correctly support the larger sector sizes and allow for dynamic adjustment of sector sizes.

You can go from 4k to 512 but not the other way. This also specifically effects data logs.