Originally posted by: SystemAdmin

I am currently setting up Power5 LPARS with dedicated FC adapters (2x FC), and will be SAN booting from these adapters but also use the same FC adapters for data access. Can I use paging space on my SAN disks for my LPARs all of which use the same set of FC adapters or should paging space be on my internal disks.

I was just wondering if my FC adapter would become a bottleneck.

thanks

Originally posted by: VirtualGreg

I'm a big fan of fibre channel boot.

The down side is your SAN architecture had better be redundant in nature and rock solid in terms of reliability and change management. If you have a SAN hiccup or single points of failure in your SAN, you're going to have more grief in an outage.

That said, with 72GB disks being the standard these days, what are you going to do with the other 68GB once AIX is loaded on internal disks? 8^)

With most SAN devices you can customize your LUN sizes and right size storage for rootvg disk(s). You can also benefit from hardware RAID with caching - any time you can rid yourself of the over head in running and managing LVM mirroring, you are a step ahead.

If your memory requirements are sized correctly, you won't do much paging I/O. I wouldn't worry about performance of paging space I/O. A disk is a disk, chances are the SAN storage uses drives with similar specs to your internal disk alternatives.

You could consider using a Virtual I/O Server for boot disks, then the VIOS LPAR's dedicated fibre channel paths take your rootvg I/O's down a different path. However, you should consider two VIOS LPARs for production workloads.

Which disk storage device are you planning to use? You should check with the vendor regarding their support and requirements for AIX fibre channel boot.

Originally posted by: SystemAdmin

Thanks for your reply, I am currently using DS4300 hence I will probably create small LUN sizes to allocate as my boot disks.

I did think about VIO server, but I was informed that the overhead of servicing both the boot disks and paging may impact my LPARs - I dont know if this is true or not.

I have an SVC, the backend is DS4300's and DS4100, but I belive the SVC doesnt support AIX SAN boot at present hence I am having to present DS4300 LUNS bypassing the SVC to my LPARs.

Originally posted by: VirtualGreg

Any I/O is a bad I/O! 8^)

If your normal application response time is 1 second, will anybody notice if it becomes 1.01 seconds?

I'm not suggesting that's the actual latency you'll see in your configuration, but depending on the workload, the benefits of driving higher server utilization thru virtualization offset the so-called "overhead".

I really don't like the word "overhead", I prefer "luxury tax". Virtualization allows you all the flexibility in the world for a few trade offs. You may notice no degradation in performance at all in terms of wall clock times.

If your paging rates are high you need to do some tuning in some cases (such as vmo options to tell the kernel to prefer stealing file pages) and add memory in others.