Sybase Question:

As always, this answer depends on the vendor's implementation on a cooked file system for the ASE... Performance Hit (synchronous vs asynchronous)

If on this platform, the ASE performs file system I/O synchronously then the ASE is blocked on the read/write and throughput is decreased tremendously.

The way the ASE typically works is that it will issue an I/O (read/write) and save the I/O control block and continue to do other work (on behalf of other connections). It'll periodically poll the workq's (network, I/O) and resume connections when their work has completed (I/O completed, network data xmit'd...).
Performance Hit (bcopy issue)

Assuming that the file system I/O is asynchronous (this can be done on SGI), a performance hit may be realized when bcopy'ing the data from kernel space to user space.