Other people should weigh in, but a RAID system keeps a copy of your files on the same hardware so if there is a hardware failure, you have lost your copy. One of the nice features of RAID systems is if a failure occurs, it is possible to replace a component drive and heal the system. I have several RAID 5 drives and have had to replace individual disks a couple of times over the years.
So, if I have a RAID 5 drive, I will back up that drive to a completely different piece of hardware (not necessary RAID 5) and store that drive offline.
I have moved to a slightly different strategy. I now use RAID 0 drives (6TB from Western Digital) and nightly do a Superduper incremental back up to a second RAID 0 drive. I also create a third copy as an archive but those only get updated monthly or so.
Those backup drives are usually useable immediately, although I may need to reconnect my aperture libary to the backup drive (apparently, Aperture is now using the UID number of the drive device rather than the drive name)
That is a common misconception about RAID. But it does NOT provide backup protection.
My backup plan is to do a backup to two external drive using different software for each one.
Then all of my photos are backed up again for third backup once more with different software since I consider them to be my most important data.
Also remember that Aperture libraries should be on locally mounted OS X formatted drives. Putting the library on the RAID is asking for trouble You might get by putting the originals there and running them referenced but even that is iffy (imo)
As for RAID as the others have said it isn't a backup system and here is why:
Lets take RAID 1 as it is the simplest and easiest to follow. In RAID 1 you have (a minimum) of two disks, each a mirror of the other. So if a file is added to one drive it is added to all the drives. If a drive dies you have all its data on the other drive. But let's say you mistakenly remove a file. Then that file is removed from all the drives, remember they are mirrors of each other. Now if you want to get that file back you can't. In a backup system, such as Time Machine, you would be able to retrieve the file.
The higher RAID levels all do basically the same thing with increasing complexity. Things like striping (writing the data across multiple drives) and parity are added.
The configuration labeled RAID 0 requires special attention. This is not really RAID in the truest sense of the term and is really more of a marketing ploy. In this configuration multiple drives are accessed as one logical unit and the data is written across the drives (as in striping above) However in this configuration there is no parity bits written with the data so, and this is the important part, if only one drive fails you will loose all your data. This configuration actually increases your risk of loosing data to a drive failure.
Why would anyone use it then? There is some speed increase in the reading and writing of data and for some applications, say video, the speed increase offsets the risk of data lose. However for an application like Aperture there is no benefit and lots of downside to using this.
And the higher RAID levels will give close to the same performance as 0 but with added safety.
For photo applications especially you need (a minimum) of) two backup procedures.
The first and most important is an archival storage of your original camera images as a minimum. If you had the room you could archive store derived images but the amount of space needed will quickly balloon and as long as you have the original you can always go back and recreate any image derived from it.
The second is an incremental backup plan such as Time Machine. This will allow you to recover images and user files mistakenly deleted within a period of time the time period determined by the amount of storage you can dedicate to the incremental backups, then bigger the storage the father back in time you can go. It will also allow you to put your system back to a know state should that need arise.
And then of course you'd be looking at multiple copies of each of the above, especially of the archival storage. So you will see people that have two copies of their archival storage as well as the on-line files (for a total of three copies) . One copy held off site.
A lot of people add a thrid which is a clone of the system disk. With a clone of the system disk in the event the system disk dies you can boot off the clone and be up in a minimum amount of time.
The possibilities are endless. It depends on how paranoid you are and how important the data is.
Yes you are correct Frank.
I failed to include the details of the backup that I listed as my third backup. It is exactly what you are suggesting here. So I feel I am covered.
I am hopeful that other who see these posts setup and test a valid backup plan.
So frequently, I have seen user setup a backup plan and never test it. Then when the data comes that data is lost all of a sudden they discover that there was a flaw in their backup plan. TEST! TEST! TEST!!
The advantage of a RAID 0 system is a 3TB x 2 is actually treated as 6TB and they are fast. But as said they are at higher risk of failure. So I have evolved to regular automatic backups of my drives.
I am not sure how the data is actually stored on a Time Machine drive and I really don't want to go through a lengthy restore.
In terms of deleted files, yep, that is always a risk.
TEST! TEST! TEST!!
Oh, how true! The test should make sure that the backup is working, not only if it exists.
- Occasionally check, if the Aperture library can be restored from the backup and if the original image files are correctly referenced.
- Check, if a vault can be restored, and if it really contains all managed files.
- Check, if the drive containing the backup of the masters/originals is still working.
- Check, if you can mount the clone, and if you can boot from it.
At least two backups are essential - I remember a scary moment a long time ago, when we had a sudden power outage during a thunderstorm, when a lightning struck close to our house. I was just doing a backup, and needless to say, both the internal disk of my MacBook and the backup disk were ruined at the same time. I could recover from that, because the desktop computer was kept in sync with the MacBook and mirrored the MacBook, so I could migrate from that machine again.
Thanks for all the info, most of which I understand, some of which enters into complexities that intimidate a feeble mind.
Now I know RAID is not a back up. Thank You.
Allen, you said, "My backup plan is to do a backup to two external drive using different software for each one."
What two software do you use?
I assume one to be the AP3 vault.
Frank, thanks for your in depth explanation of your backup strategy.