Not sure you should change the blocksize... FBA devices are natively 512B blocked, and I'm pretty sure the FBA discipline of the DASD driver knows this.
Does not make a difference. The FBA discipline ignores the CMS formatting completely and simply overwrites the disk with what it likes to do. This way to swap is not very efficient however. What you want is used the diagnose discipline instead. One thing to do that indeed is CMS format with 512-byte blocks *and* make sure the diagnose discipline is enabled before Linux detects the disk. Unfortunately the SuSE SLES8 kernel does not have it like that, so you either build the kernel yourself with the proper options or play with /proc/dasd/devices and modprobe a bit. The diag mode with VDISK will give you impressing swap rates.
Rob (I predict an upcoming redbook will show this ;-)
