Setting up Raid for 2 HDs

1. Go to your Utilities folder, find Disk Utility, and then select one of the HDs you want to use for the raid, select RAID, select what level of RAID you want (striped/mirrored) set, and then follow instructions (Aka draggin' discs/volumes into Disk Utility's Box). Backup before you do anything.

2. Generally scratch drives are only used for data - the OS and Application reside on a separate disc.

There are several levels of RAID. JBOD (Concaternated?) stands for "just a bunch of discs", in which the two discs just get added on top of each other, with no speed increase or redundancy. RAID-0 is the speediest array type the data is "striped" along the hard drives - practically doubles the read and write times. RAID-1 doesn't increase write times, but if one drive fails, you still have a data. RAID-0, one has a hard drive fail, all data is lost and one has to resort to backup. Note the RAID-1 is not backup, merely redundant.

Those are the software levels of RAID that OSX can provide, IIRC (Besides 10 and 01, which the numbers correspond to the levels I just mentioned). TO get more advanced RAID levels (RAID 5, 6, etc.) one needs a RAID card... etc etc. By then its a question of the amount of investment.

I would recommend reading Wikipedia's article on RAID, specifically levels zero and one as those are the ones OSX provides free of charge.

 

1)Make sure that you have a good backup of the data that is currently on one of the drives because creating a raid volume involves formatting.

2)Go to disk utility -> click the drive you want to create a raid with -> go to the raid tab -> choose what you want to name it, the filesystem and size.

3)Make sure you choose striped raid set not mirrored.

4)Add the drives you want to include in the raid set and create it.

 

If your RAM capacity is too small for the system to handle your jobs in RAM it will use scratch disk to handle data. So one important question is how much RAM does your system have. If you runs 32 GB of RAM you are unlikely to need much scratch disk. If you run 6GB it is much more likely you need it. In a Mac Pro it would make sense to use a separate disk and cut off the fast top slice of it for scratch disk. With your RAID0 I would not do this because it would slow down the system and apps that usually take the fastest slice of the array because they get installed first.

 

Your Raid0 is likely to be your fastest drive unless you have an SSD. So I would recommend to use it for system, apps and data. Load the system and apps first to get them on the fastest parts of the array. The disk that you will free up can be used for scratch disk. You may partition it and use the rest for data as well.