pdagamer yes you are right for reading from RAID 1. A well designed controller will split the read requests to different disks. Very perceptive of you. Few people realise this.
I also like the way you think wrt the RAID being secure. I never thought of that. Very clever. Who is this guy? Do you work for NSA or something?
To answer your questions oblivion, yes you will get a speed up of roughly 1.5-1.8x over a single disk and yes os loading, program startup, moving files will all speed up significantly. Any games that require disk access during play such as Max Payne 2 or Uru which reload maps etc will work faster during the disk access.
Slowdowns due to disk half full - yes and no. This can happen due to two things.
1. fragmentation of the filesystem on the disk
2. older style (FAT/FAT32) filesystems.
Note formatting involves two steps but one program within Windows - first write sector header info, then write the file system. Unix/Linux separates the processes into distinct programs.
When the file system is first created all blocks on the disk are contiguous ie. there are no gaps between chunks of available storage.
As files are added to and removed from the file system the available space gets chopped up into smaller and smaller chunks (entropy always wins for those of you with a physics background
). Sometimes small chunks will adjoin each other and be reused as one large chunk but things get worse the longer the file system is used and if there are lots of small files stored/deleted. With older filesystems, such as FAT/FAT32 their ability to co-alesce smaller chunks is limited. As the disk fills up the space allocation algorithm finds it harder and harder to allocate chunks of disk to the files. Hence the user perceives this as a slow down in performance. To rectify this people will often de-frag (de-fragment) their filesystems. This runs a special program over the filesystem and reorders the sequence of allocation of files, thus co-alescing smaller chunks into bigger ones and sorting out the indexes into the filesystem.
More advanced filesystems such as NTFS (Win2000/XP), UFS (Unix File System), ext3 (Linux), AdvFS (DEC), Veritas etc don't suffer from this allocation problem so don't slow down as much as the disk becomes more fragmented or full.
If you are doing video editing I would highly recommend RAID 0. Since the applications tend to move large amounts of data to and from the disk it will definitely help. Just make sure you do a consistent backup to an external disk on a daily basis. That is just good practice irrespective of using RAID 0 or not.
One futher point - make sure that you use NTFS as the file system for your video files. The file size limit on NTFS is *much* bigger than FAT32, so you will not be forced to split large video assets.