A RAID mirror set (which consists of 2 physical drives) appears to the system as a single drive. When you create the RAID mirror set, you will give the mirror set a name, which is then the drive name. The RAID mirroring process automatically duplicates the same data on both physical drives invisibly & simultaneously. If you wanted to use the RAID mirror set as your FCE scratch disk, you would only have one FCE scratch disk, not two.
I would not advise using two separate external drives as a RAID mirror set. The only way to do this would be through software, specifically in Disk Utility. This is (imho) a much riskier RAID mirror than having a hardware-based RAID mirror (a 2-drive enclosure where the mirroring is all hardware based in the enclosure).
Also, RAID mirroring is not a substitute for backup or archiving. Yes, it protects against a single physical drive going bad, but the set is online, it is not offline backup. And more data gets destroyed through user error or software error than by physical drives failing. So, separate, external backup is equally if not more important than having a RAID mirror.
Thank you Martin for your thorough and helpful reply. I appreciate your insights and advice.
I omitted to mention that I have one new 2-TB drive and a year-old 1TB drive that I am planning to use for FCE scratch discs. From your response, it seems that I would do best to specify them both as scartch discs in FCE settings, and not trouble with mirroring. I just wanted to confirm that, please, before going ahead. Thanks, Keith
Using 2 drives as FCE scratch disks does not provide any better protection against data loss than only having 1 drive. FCE would use the first scratch disk until it's full, and then start using the second scratch disk. There would be no backup.
My advice is to use one drive as your FCE scratch disk and the second drive as backup. You could manually copy your clips & project files to the backup drive, or use something like CarbonCopyCloner to automate the backups.
(And by backup, I am not suggesting the use of Time Machine as your backup. TM is a great thing, but it's still an online drive and in my book that's not an effective backup plan. True backup needs to be offline except for times you are actually doing backup & restore operations.)
Ah, this is getting more interesting. Thanks for the info on the way the second drive is used. I now see the value of a manual back-up on the second drive.
How would I do that to ensure that the project and all the associated media files are there in case the first drive fails? Is it just a matter of periodically saving the project to the second drive from FCE while working on the movie, or dragging and dropping the latest "copy" in Finder? I would want to be sure that I was saving everything to keep the integrity of the project. I am dead scared of those horrible bright-red "media offline" images in the Timeline!
Thank you for clarifying about TM: I'm beginning to see it's limitations in the case of iPhoto back-ups too.
Thank you, Martin, for following up on my enquiry; sorry it is all such basic stuff. Keith
You could do one of the following:
- Use the Finder to periodically and manually copy a) the entire Final Cut Express Documents folder or b) everything except the Render Files or from your scratch drive to your backup drive. The problem with this method is you end up manually copying everything every time. Of course, you could get away with copying your source media clips just the first time you back up manually, but then you have to keep track of everything yourself because you may add more clips as you go along.
- Use CarbonCopyCloner (free) or a similar utility to automate the backup/synchronization process. It takes a little learning & practice to set up the first time but afterwards you can schedule CCC to run periodically, or on demand. Doing it this way you can set parameters on how to handle duplicate files, files that have changed, exclude certain folders (eg the Render Files folder) etc. from the backup and other things.
There are additioanl possibilities but these seem to be the simplest to me.
Sorry to keep on about this, but I am still unsure which way to go. I do not mind paying the $40 for CCC but I have looked at their site and it all seems very complicated. Would I be able to simply set it up so that my whole current project is duplciated on a second external HD so that, if the main scratch disk fails, I could then access the project with all its necessary underlying media files?
I have tried copying the projects at different stages of completion, ie when finished and rendered in Timeline, just after I make a QT movie and save that, and after making a movie in iDVD but all I get is the "shell" of a movie which tried to open in FCE but it has no media, just red boxes. (just the iDVD theme plays, not the movie.)
As an alterantive, I would not mind the manual method mentioned above, but I wonder how I could be sure that I was saving the entire FCE documents folder each time? Is it easy to identify everything needed from the scratch disk?
Thank you for any advice you can provide. Keith