There are a lot of things to consider. What's important is how is the data being used, and how often. More reads than writes? Large sequential accesses, or a gazillion short reads/writes all over the place? What's your backup solution? Do you have a need for business copies? And if so, do you need to be able to split of a mirror (almost) instantaneously? How many boxes need to see the disks that form the database? That is, does Oracle run in a cluster, and if so, of how many nodes?

Things that will influence your I/O performance:

• FC vs. SCSI.
• If you have FC, the fabric and the switches involved.
• Number of controllers that can access the data.
• Other traffic going over the same controllers.
• Your storage box (from just a bunch of disks to large storage devices like an EVA or an XP)
• Size of all the caches and buffers involved.
• Number of spindles.
• RAID settings.
• Setup of your hot/warm spares. (This, together with the RAID settings may have an extra performance impact when one or more disks have failed)
• Size of the disk and its frequency (rpms).
• Synchronous or asynchronous access.
• LVM settings.