> On one hand using ECKD will get us some CPU cycles back due to more > work > being done by the SAP, but just recenly I heard that IO can be faster > (higher throughput) with FBA/SCSI.
Not likely. The ability to drive up to 16 200MB/sec paths full on is very valuable, as is PAV. > > I'm assuming there's no clear answer as to which is best, because like > so > many performance tuning things, the answer is always "it depends". > > But, what are other people doing? My general recommendation these days is ECKD for performance-sensitive data, FBA/SCSI for volume of data. Apps with large amounts of data tend to want multiple-hundred gig volumes, and that's just a nightmare to deal with using LVM. If you've got users expecting real-time response, then the ECKD route blows the FCP stuff away. If users want more than about 100G filesystems, use FCP/SCSI storage. The second decision (if you go FBA/SCSI) is raw FCP or EDEV. I prefer EDEV because it's a lot more natural to the VM world and tools, but there is a performance impact due to the necessary CPU consumption of the EDEV emulation. Last decision: can you afford the ECKD/FICON adapters in your storage units? They cost about 5 times as much FCP adapters for the same storage units. If you do FCP storage and/or EDEVs, you can reuse existing FCP adapters that may be free on your SAN. That's how we decide what to put where. YMMV.
