Differential

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Differential

Postby badams_ios » Thu Dec 06, 2018 7:19 pm

Isn't there a way to tell the IFW to make a differential rather than an incremental?
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Re: Differential

Postby TeraByte Support(PP) » Thu Dec 06, 2018 8:46 pm

They are both Changes Only backups. Base on the Full image for a differential chain. Base on the last incremental for an incremental chain.
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Re: Differential (vs Incremental) Backups

Postby Muad'Dib » Thu Dec 06, 2018 10:03 pm

I've been using IFW for so long, I just know how to do it, but looking back, it's not that obvious from the documentation, especially since the explanation of the concepts of incremental vs differential are near the end, in appendix B, while the actual backup steps are described in the section titled "Creating a Differential or Incremental Backup" starting on page 58 (of the IFW manual at the time I wrote this post). Going back and forth between the two sections is not necessarily that friendly for a newbie. So here's my attempt at explaining it in more user-friendly terms:

For DIFFERENTIAL: You choose "Backup" and then "Changes Only" and then when it asks for your "existing backup file", choose the full backup .TBI file you created. The next time you want to do a differential, you do the exact same thing. Each time, your differential file will be larger than the previous one, and will only refer back to the original full backup file you created. So for normal backup purposes, once a new differential file is created, you can delete the previously created differential file, though you may want to save it for awhile, just in case your most recent differential file just happens to become corrupted, you could always use the next most recent one (but if you do this, your backup won't contain the most recent changes).

For INCREMENTAL: For the first time, you do what I said in the first sentence of the above paragraph (there is NO difference between the first differential and first incremental). However, the next time you want to create an incremental backup, instead of choosing the original full backup file as your "existing backup file", you choose the most recently created incremental .TBI file. Each incremental file will be of varying size (depending on how many changes were made since the last incremental backup). For incremental backups, you need to keep the original full backup file and ALL of the incremental files in order to perform a successful restore (until the time when you perform a new full backup, then you can delete (or move) the previous set of files). Again, with the warning mentioned in the previous paragraph about keeping some old backup sets in case the most recent one is corrupted somehow.

During restore, you choose the LAST (most recent) file created (either the last differential or last incremental). If all the files are in the same folder, the program should automatically find the previous files in order to perform a complete restore. If they are in different folders (or if you moved the files), then after first choosing the most recent backup file, the program may ask you to point to the location of the "next" backup file (by "next" it actually means the PREVIOUS file in the historical chain). If you happen to choose the wrong file, the program should recognize it as such, and ask you to choose a different file.

If all of the above is confusing (and even if it isn't), I recommend trying to create some test backups of a very small partition (just so it doesn't take that long), and trying out the different types of backups of that partition. If you've installed TBIView, you can then click on the different .TBI files you've created, and the program will display the contents of your backup (and if you've made changes to the partition in-between backups, you can see those changes, depending on which backup file(s) you select to view). You can even move some of the backup files and see how TBIView asks you to find the "next" file(s) in the chain. This will be similar to what happens if you need to restore a multiple chain backup set.

If you're really brave, you can try to restore as a test - BUT RESTORE TO AN EMPTY EXTERNAL DRIVE (this way, if you make mistakes, you don't overwrite the original partition).
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Re: Differential

Postby badams_ios » Fri Dec 07, 2018 11:25 am

Good advice. I already know I want differential but I don't see how to tell it to to a diff. Seems to default to inc. Only. Where do I change it. I'm asuming it's a switch but my eyes are crossing from reading the manual.
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Re: Differential (vs Incremental) Backups

Postby Muad'Dib » Fri Dec 07, 2018 11:37 am

There is no switch. You choose "Backup" then "Changes Only", then which type of backup is performed depends on which file you choose when Image asks you for the "existing backup file":

Image does a DIFFERENTIAL backup if the "existing backup file" is the latest full backup .TBI file. The file that is then created contains the differences since the FULL backup. You must keep the last full backup file and the last differential file since the last full backup in order to perform a successful restore (previous differential files for that backup set can be deleted). A differential backup set will contain the last full backup file and the last differential backup file (two files at most).

or...

Image does an INCREMENTAL backup if the "existing backup file" is the latest incremental .TBI file. The file that is then created contains the differences since the last INCREMENTAL backup. You must keep the last full backup file and ALL incremental files since the last full backup in order to perform a successful restore. An incremental backup set will contain the last full backup file and ALL the incremental backup files created since the last full backup (no specific number on how many).


IMPORTANT NOTE: The above explanation assumes your File Size (in the Backup Options screen) is set to "Max". In other words, you are NOT splitting your backup file into smaller files in order to fit them on external media (CD, DVD, etc.). With multiple smaller files, the above explanation is still valid, but I would have to rephrase things to take into account that each backup creates more than one file (and that would make the explanation more complicated).
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Re: Differential

Postby badams_ios » Fri Dec 07, 2018 12:33 pm

Let me make sure I understand. I want a full backup Fridays, and diff Sat thru Thur. I could do a full backup manually, then go back and choose changes and select the full backup to compare to. Then setup another change backup and as long as I select the full backup it'll backup changes from the last full. Then I can delete the 1st changes files. Is that correct?

Otherwise if I want inc. instead of diff. I select the most recent change to compare to?
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Re: Differential (vs Incremental) Backups

Postby Muad'Dib » Fri Dec 07, 2018 12:55 pm

I think you have it, but here's another way to explain it (the file names (FRIDAY-F1, SATURDAY-D1, SUNDAY-D1, etc.) are simply what I'm calling them for the purposes of this post, you can name them whatever you want to keep track of things):

DIFFERENTIAL (D):
Friday - choose Full - creates file FRIDAY-F1
Saturday - choose Changes Only ("existing backup file" is FRIDAY-F1) - this will create file SATURDAY-D1.
Sunday - choose Changes Only ("existing backup file" is FRIDAY-F1) - this will create file SUNDAY-D1 (SATURDAY-D1 is no longer needed).
Monday - choose Changes Only ("existing backup file" is FRIDAY-F1) - this will create file MONDAY-D1 (SATURDAY-D1 and SUNDAY-D1 are no longer needed).

And so on... Until next Friday when you choose Full and create file FRIDAY-F2.

INCREMENTAL (I):
Friday - choose Full - creates file FRIDAY-F1
Saturday - choose Changes Only ("existing backup file" is FRIDAY-F1) - this will create file SATURDAY-I1.
Sunday - choose Changes Only ("existing backup file" is SATURDAY-I1) - this will create file SUNDAY-I1 (you'll also need FRIDAY-F1 and SATURDAY-I1 for a restore).
Monday - choose Changes Only ("existing backup file" is SUNDAY-I1) - this will create file MONDAY-I1 (you'll also need FRIDAY-F1, SATURDAY-I1 and SUNDAY-I1 for a restore).

And so on... Until next Friday when you choose Full and create file FRIDAY-F2.

Does this make sense (and match what you were thinking)?
Last edited by Muad'Dib on Fri Dec 07, 2018 1:13 pm, edited 1 time in total.
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Re: Differential

Postby badams_ios » Fri Dec 07, 2018 1:12 pm

Yes, however, how does task manager know when it's a new Friday?
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Re: Differential (vs Incremental) Backups

Postby Muad'Dib » Fri Dec 07, 2018 1:14 pm

What do you mean by the task manager? Are you talking about scheduling a backup to perform automatically? Or something else?

UPDATE: I have to leave, so I'll be away from the forum until tomorrow (possibly sooner, but I can't promise). Hopefully you have enough info, or someone else can continue to answer your questions.
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Re: Differential

Postby badams_ios » Fri Dec 07, 2018 1:22 pm

Yeah, I meant the scheduler. Doing too many things at once.
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