Can I have 2 RAID arrays?

Ehm, you need at least two drives to make one RAID.

 

You can have as many raid arrays as you have drives/controllers so yes.

I ran a raid 0 2x400gb for OS and programs and a raid 0 2x500gb for files for the last 2 years.

If your going to keep your files on a raid 0 array you MUST keep them backed up on something like an external drive. The odds of loosing your data are twice as likely with raid 0

 

It's quite possible, but there are limitations, such as the drive count as mentioned (port count sets the max possible), but assuming you mean to do this via OS X's software RAID utility (found in Disk Utility), then the array types are limited to 0/1/10.

 

When dealing with a stripe set (RAID 0), you get the throughput of a single drive in that system * n (model to be used for RAID, and presuming they're all identical).

So if the intended drive is producing 100MB/s, a set of 2x will produce 200MB/s.

The purpose is to keep a system running even in the event of a drive failure (data is still all there, and is available, though it's running slower). Some levels can provide this, but a stripe set CANNOT. In the instance of a stripe set, if it goes down, the array is done until it's been repaired, and the data must be restored from a backup. You need backups regardless of the array type used, so please heed this bit of advice. RAID /= Backup. Period.

You can use a second RAID as a backup of a primary RAID, but it's still a backup. The primary (no matter the level used), can get to the point the data is just gone (i.e. RAID 5: a drive fails, you replace it, and the array begins to rebuild, but there's another failure during the process - it's done for, and you would have to restore from a backup).

A redundant array can also save you time as you don't have to repair, reinstall the OS (assuming the OS resides on the failed array), and restore the data (assuming you catch it in time, get a new drive in, and let it rebuild). It would be available during this time, but it increases the stress levels, and is advisable to let the rebuild complete before attempting to use the system.

Ultimately, it's up to you to determine if your data is important enough to warrant a redundant array though. But as a general rule, if you're making money with the system, it's highly advisable (you won't have to re-perform all the missing work, as there can be gaps between the last file updated/created and most recent backup/s).

 

ProTools doesn't support storing session data on a RAID. You can search other forums about this, but I would strongly encourage you to have a separate non-striped disk for storing all of your ProTools sessions and associated files.