What block size should I use when creating a database? 

To begin with, the answer to that question depends entirely on the answer to another: are you using buffered I/O or not?

If you are buffering your I/O (that is, your file system has its own buffering mechanism, as most do by default), then your Oracle block size should match your file system’s buffer size exactly. For ext3, for example, that would mean 4K blocks by default, whilst for Tru64, it would mean 8K blocks -because those are the buffer sizes for the respective file systems. NTFS, by contrast, is a little unusual for mainstream file systems in that it does not have its own buffer, so reads from and writes to a volume formatted with NTFS are done directly -and at that point you can pretty much pick any Oracle block size you like.
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