I'm trying to figure out if there's some way I can tell if a system is being adversely affected by disk misalignment -- i.e. when I do a disk I/O operation, it actually needs to request extra blocks from the back end storage (we're using a SAN) because the requested block of data actually lives on multiple blocks on the actual disk.
This problem allegedly affects VMs even more, as the disks are abstracted so that blocks don't align because of improper sector offsets, causing additional IOPS to be used when accessing the backend storage from the VM.
Anyway, I've been looking at iostat output, and it seems like there's data there that might give me a clue to this, but I seem to be slow at reasoning through it. Is there some clue to indicate with iostat (or something else) that the machine might be performing more disk I/Os that optimal?
(I'm not convinced that disk alignment is worth the effort to investigate/worry about, but I would love some opinions on the matter!)