Difference between "Image" and "Backup"

[freak393]

Hello,

 

I'm trying to really dig myself into the whole "science" of making backups.

 

BUT, there is on thing with regard to Retrospects back up procedure which I do not fully comprehend:

 

There are many disk imaging tools out there which create complete images of drives. Images are, as I understand, the most "complete" way of backing up a drive, it's everything...

 

Retrospect allows me to create backups of my drives but seems to avoid the term "image". So, what exactly is the difference between an image the complete drive backup used by Retrospect? What are the (dis-) advantages?

 

And: can I use a complete Retrospect drive backup to restore the backed up computer on a new blank disk (with the same hardware as before) as I could with an image?

 

I know that with a backup as well as an image I can restore individual files.

 

Thank you very much for your help!

 

Regards

[rhwalker]

A backup preserves history. An image is the state of a disk at an instant without history. That's the difference.

 

Backup programs make a "full" (complete) backup followed by incremental backups that record only the changes. Retrospect's difference from other backup programs is that it presents a "snapshot" paradigm, which is the accumulated set of changes as if you started with the "full" backup and then applied all of the successive incremental backups, replacing/deleting/creating files as necessary to end up with the drive state at the time the "snapshot" was taken; but the underlying mechanism is full backup plus incrementals, just like other backup programs.

 

It's actually more complex than that, both with imaging and with backups, unless you image or backup a quiescent disk, because backup is done on a file-by-file basis, and there may need to be a group of files that has to be self-consistent (such as an email database), and because imaging is generally done on a sector-by-sector basis (such that there may be filesystem corruption if filesystem structure is imaged while it is changing).

 

But the real difference is that backup preserves history, imaging is an instant in time.

 

Hope that clears things up.

 

Russ

[freak393]

Thanks a lot Russ.

 

That did help indeed.

 

Maybe you can help me out once more.

 

I now understand that with both types of backup (image and full disk) I can restore a system on a blank hard disk. Right? Does this also cover the case in which I have to install a new but possibly different model of hard disk (e.g. total failure of the old hard disk)?

 

(A backup might even be more safe as the backup is done on a file, rather than sector basis eliminating the chance of imaging defective files due to unrecognized bad sectors or changing sectors at the time of creating the image.)

 

I assume you will say "Not quite" as with images (as well as with full disk backups of for example Acronis True Image 10 Home which does images and backups) you put in a disaster recovery CD, boot from that and restore the system.

With Retrospect however, I'd have to install a temporary OS (which will be overwritten on restore) before I can do that, right?

 

Can you give me an insight on why that is - isn't the competitors approach superior i.e. much less time consuming? Especially as you can access usb and network devices straight of the disaster recovery interface?

 

I must say the while I am sympathizing with Retrospect due to good reviews and other peoples feedback it "feels" harder to understand than some other programs. "Might" just be me

 

Your help is much appreciated!

[rhwalker]

Quote:

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With Retrospect however, I'd have to install a temporary OS (which will be overwritten on restore) before I can do that, right?

 

Can you give me an insight on why that is - isn't the competitors approach superior i.e. much less time consuming? Especially as you can access usb and network devices straight of the disaster recovery interface?

 

---

It's because Retrospect is a file backup/restore program that puts you (well, almost, unless you back up a quiescent system) to the same place you were at when you did the backup.

 

I'm not going to debate competitive issues. The product is pretty good at what it does, and it serves our needs. It may not serve yours. Again, imaging is not backup because it has no history.

 

FYI, there are many ways to do imaging, too, including an instantaneous way that keeps servers up 24/7/365. If you want to explore that approach, search the forums here on my username and RAID to understand a RAID 1 mirror split. Again, it's not a backup; it's an image, and it serves a different purpose. Each has its place.

 

And our offsite Retrospect backups saved our firm's data when a fire wiped out our floor of our building a couple of years ago. We lost all of the computers, but did not lose any data. And Retrospect allows us to restore any machine, any file, on any day back to 1992. That's more than imaging could do, unless you've got a warehouse of drive images.

 

Russ

[dg27]

Thanks, Russ for the informative post. I've been using Retrospect 7.5 Pro on my two desktops, backing up each one twice a week. Had a hard drive failure in February on one machine and although I eventually did restore my data, it was a lebthy process apparently because the partition parameters were different on the new hard drive than they were on the drive that died. I had a lengthy post about it [http://forums.dantz.com/ubbthreads/showflat.php/Cat/0/Number/94982/an/0/page/3#Post94982], but never really got any conclusive answers as to how to complete the restore. [A Retrospect tech told me by phone that I had to "massage" the reinstall to fully accept the backup sets. ] I ultimately restored my data to an external drive, but did have to reinstall XP Home and all of my programs. One big blunder on my part probably was that I had not created disaster recovery CDs, something I'll try and do this weekend on bothy machines. Would that have made a difference? How long does it typically take?

 

A tech I consulted did suggest Acronis, but your comments do make me wonder.

 

dg