If you have small files, a large block size will cause more space to be wasted. On the other hand, a block size that is too small may cause the filesystem to use large amounts of space for internal metadata, especially if the filesystem uses simple tables for tracking block allocation.
So the optimal block size depends on the kind of files you'll be storing and the internal structures of the filesystem.
Increasing the block size is just a simple way to "extend" the range of disk sizes the filesystem can handle without significantly updating the filesystem technology.
With VxFS layout version 6 and above, you can create a filesystem of 32 terabytes in size while using the default block size of 1k.
If you increase the block size to to 8k, the maximum filesystem size will be 256 terabytes.
According to some documentation, you may need something called "EBFS license" to create filesystems creater than 32 TB. That same documentation said the current supported maximum size is 40 TB (i.e. that was probably the largest configuration HP had tested and found good at the time of writing that documentation).
If you need to create >32 TB filesystems and your system is covered by a HP support agreement, it might be a good idea to talk about this with HP support first. They may have more information about latest supportability tests than is publicly available.
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