Atroz: That is a very good rundown on specifics, but some of those issues have other solutions.
1) You must disconnect the second drive else you run the risk of whatever causes data loss on the first drive doing the same to the second.
That is why I use the mobile rack . . . each one has a key switch on the front that makes that easy.
2) If your backup media is disconnected, it is impossible to do automated incremental backups.
OK . . . valid point . . . my system does that differently. I have LS-120 drives in every computer, and that is done on a 120 MB SuperDisk, and those are interchangeable from computer to computer.
3) You have to reboot before and after each backup to remove the second disk
Reboot yes, but remove not necessarily. DC 3 hides the backup drive when finished so that it is not seen.
4) You only have one complete copy of your data, no history of files.
That is for the LS-120 backup data files. My primary concern is operating system and software redundancy and recovery in just a few minutes.
5) The mobile racks is a good idea, else you run the risk of damaging the drive or cables with repeated insertions.
Also, a good mobile rack will have a male-female Centronics connector internally . . . they mate properly with less precision required, and are thus more reliable and rugged.
6) Cost. I can do a complete backup of all my data for a few dollars, and do it again next week, and the following week, etc... Yes, I need to have a CDRW drive, but they are useful for other things too. This is why I've given up on tape, it's only really good for backups.
A second 20 GB 7200 HDD now costs only about $135. Rack mounts are about $15 to $25 each. Yes . . . CDRW has other uses. I have two of them, but even at 12X they are slow, and if a HDD problem does occur all you have is a disk that won't play anything until you restore the system with a new HDD or new installation of the old one after FDISK and reformatting. Costwise, that to me is major . . . you're talking hours of work.
7) If you want off-site backups, then the HD method becomes even more costly and inconvenient.
Mentally, I'm not ready for that except for additional copies on LS-120 disks. But, that is a valid point for dupe HDDs only.
8) No cheap offline storage. I.e. Collections of digital photos of your family, etc.
That is what I use my CDRWs for . . . permant storage of digital imagery, but that is not a system backup. CDRs are also very cheap and cheap to mail . . . 55 cents in a padded bag.
9) Ties up a HD connector.
Have never found that to be a problem. Always have two HDDs on Controller 1, LS-120 and CD ROM on Controller 2. CDRW and scanner and 2nd CD ROM drive on SCSI external. Other devices on USB and IEEE 1394.
10) For longer term storage, HDs are likely more prone to data loss and environmental damages.
Possibly, but in the past 18 years, I have only experienced two hard drive crashes. One was due to a lightning strike power surge. Since then, all systems are on 650 VA UPS's, and since installing them (3 years ago) have not had a problem of that nature.
I would say that the decision on which way to go depends on the primary pobjective of backup. If it is just data, and incremental additions, then removable media is best. My primary objective is system redundancy with no down time.
It also makes experimenting with new products and beta ware a no risk operation. Prior to the experiment, do a fresh drive copy. Takes only 12 minutes for a 20 GB drive. Then try the new stuff. If it bombs your system, then swap drives and you are immediately restored. If it works, then you can either keep the previous system or transition to the new one.
These are all good thoughts, and make for a thorough discussion of the entire backup panoply. I agree that tape generally sucks . . . slow and restoration is painful and iffy at times. CDRs and RWs are very good, but only hold 650 to 700 MB of data. That is great for data, but not good for system backup complete with all software installed.
Add to all that the possibility of a LAN. I have 4 units on mine, and that is another data backup capability. I synch the data on all units automatically every night, so there lies another system redundancy.
There is another hidden benefit of all this backup redundancy . . . it seems to scare the s--- out of all units so they never crash, lockup or give me BSDs. I guess it relates to an umbrella . . . caryy one and it never rains.