Hi
coolcorgi. I thought I'd address each of your queries in turn so that you're completely clear. Sorry
ChrisA if you think I'm stepping on your toes.
Two things to point out: first, I realise that you're not the Original Poster for this thread, so I'm not going to assume that you're in exactly the same position as
skyneedle; second,
ChrisA's proposed system is admirable and very thorough, however many private users would find his system overkill and too pricey for their needs. I'm not saying that that's your position, however, just wanted to warn you.
OK — point by point:
the old backup is overwritten and.....???? - "does not count while a backup is in progress. You need four copies if you plan to overwrite a backup" - ????.....
So,
ChrisA is advocating having at least three copies of your data: the primary copy (the original on your computer's hard disk) and two backup copies. However, he suggests that if you're using a rewritable medium to perform your backups (e.g. Hard disks, DVD-RW) then while your computer is actually making the backups, only two complete copies of your data exist (the original and the other backup). This, he suggests, isn't suitable (since you no longer have three copies of everything all the time) so you need to have a fourth copy of your data to satisfy the three-copy minimum (original, two backups and the third backup being performed).
you must keep a ..... ???? - "HISTORY of your file system. Perodic full copies are not effective". - ????..... Reason: If a .....???? - "file is lost and then you make a full copy of your system now your backup has a lost file too" - ????.....
If you use software like the excellent
SuperDuper, your backup system will be the software making a mirror of your main drive onto another hard drive: the backup copy (copies) would be a 'snapshot' of your main drive at the time the backup was made. However, what if you deleted a file from your main drive, then performed a backup, and then realized that you needed that file again? The file would have been erased from the backup as well, since the backup copy is simply a mirror of your main drive at a given moment in time. However, if you use software such as that formerly known as
Dantz Retrospect (equally excellent in my experience, but it can be complicated and can be expensive, and others
loathe it), it keeps archived copies of your data in your backup system, with the result that you can go back to a version of a file from several generations ago, even though you may have made several backups since then. Doing backups like this obviously requires more space for your backup, however.
use any media type you like. Portable hard drives, CD or DVD ......???? - "but don't expect any of this to last a long time. It will all die in a few years." - ????..... you must rotate new mdeia into your system.
In other words, all media die, whether they be CD/DVD or Hard Disk. Therefore you should work out your own 'media rotation' cycle so that you replace old disks in your backup set before they have a chance to die on you. A dead backup is a worthless backup, after all!
Next you can attach a good sized external drive and .....???? - "program a daily incremental backup." - ????..... If you have a Mac Pro I gues you could use an internal drive for this.
An 'incremental' backup is one where the backup software examines your main drive and only copies the files to your backup drive(s) which have been changed since the previous backup. If you 'program this to happen daily', then it would happen automatically daily so that your backup set is always up-to-date within a margin of 24 hours. An incremental backup is very useful when used in conjunction with software like Dantz Retrospect, which I mentioned before, since it is effectively 'archiving' previous versions of your files.
Lastly you .....???? - "primary storage could be a RAID system" - ????..... if you like
WHAT DO YOU MEAN BY "PRIMARY" - I assume "RAID" is software?
Oh, boy, RAID, joy. OK — RAID stands for 'Random Array of Independent Disks' and can either be controlled by software (your operating system — RAID support is built in to OS X) or by a hardware card. RAID is essentially a system whereby multiple physical hard disks appear to the OS as one contiguous drive. There are different setups for RAID, although two are the most common: either you set it up so that streams of data are split up and written to multiple disks, with the result that your drive-access time is much faster (since multiple disks are doing the work of one drive)—this is called 'striping', since data is written as 'stripes' across many disks; the other common RAID system is 'mirroring', where each of the disks in the array stores exactly the same data, with the result that if one disk goes bad, then the other disk still has all your data; you can drop in a new disk to replace the failed one and the data is automatically copied to it and everything is kept in sync. This is
not a suitable replacement for a backup, however (for the same reason that just overwriting snapshots is not a suitable backup).
By 'Primary' I think
ChrisA is suggesting that you could use a RAID system as your main drive.
You can read up on RAID on the Wikipedia, and there's lots of other information about it all over the Web.
you must archive NOT just the .....???? - "current state of your system but also older snapshots of it". - ????.....
This is going back to the point earlier about not just making snapshots of your data, but keeping incremental versioned backups. In an ideal backup methodology, you would be making backups (at least two, if not three, remember!) with a versioned incremental system where there may be multiple versions of any given file included on the backup disk. Then, periodically, say monthly, you would make a complete snapshot of your drive on that day and store that on removable media such as DVD-R; that way you would build up an archive over the years of the way your system looked month by month.
This is all pretty complicated stuff. Effectively, you need to work out a backup system that has enough inbuilt 'redundancy' to cover you if any kind of disaster strikes (hard disk failure, theft, fire, storm: therefore it makes sense to keep copies of your data offsite). I hope I've been of some little help, and haven't served only to compound your confusion!
Richard
PS I'll let someone else explain how to do comments in BBCode. I didn't want to keep all the fun for myself.
