Create Sector Hash Files default in 3.18

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Re: Create Sector Hash Files default in 3.18

Postby rseiler » Tue May 29, 2018 7:49 am

I hadn't looked at my differential dir yet this month. When I did, I was surprised to see each diff backup accompanied by hash files.

Correct me if I'm misunderstanding something, but the way that I've been using hashes all these years was that it was created with the full backup ONLY. Differentials would them come along and reference *that* hash, not create their own each time.

So, if that's right, and if the hash is going to default to on, it should know to default to off when the backup is not full. Right?
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Re: Create Sector Hash Files default in 3.18

Postby TeraByte Support(PP) » Tue May 29, 2018 9:36 am

When there were only differential backups that was the case. However, with Incremental backups it wouldn't know if you were creating a differential or incremental backup (they are both the same at the full/base point) and it wouldn't know whether or not you planned to use the backup being created as the base for a future backup.

If you have the differentials scripted you can add the /hash:0 parameter to the command to disable the hash files.
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Re: Create Sector Hash Files default in 3.18

Postby rseiler » Tue May 29, 2018 10:03 am

I don't really follow that second sentence, mostly because I don't understand how an incremental backup could ever be used as a base. But I don't have experience with incrementals to know.

I know when creating a differential that you must use /base. Is that not also the case for incremental? I was just thinking that IFW could check for the presence of /base in a command line, and if it finds it, default to /hash:0 (or, conversely, look for /d before setting /hash:1).
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Re: Create Sector Hash Files default in 3.18

Postby Bob Coleman » Tue May 29, 2018 10:43 am

When you create a full backup and then a changes only backup using the full as the base, the result is either a differential or incremental depending on how it is subsequently used or not used.

You can create the full, use it as the base for a changes only and then later use the changes only as the base for another changes only thus starting a chain of incrementals.

In this case the hash files have to be created when creating the first changes only in order to get the benefit of them when using that changes only as the base for the next changes only.
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Re: Create Sector Hash Files default in 3.18

Postby rseiler » Tue May 29, 2018 12:14 pm

Wow, I think I actually followed that. Creating a chain of incrementals sounds potentially problematic, but I see now why you can't discern on switch use alone.
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Re: Create Sector Hash Files default in 3.18

Postby Bob Coleman » Wed May 30, 2018 2:46 pm

For whatever it's worth, I create a full backup once a week and an incremental on each of the following six days. So far, I've never had a problem picking any incremental and restoring from it.
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Re: Create Sector Hash Files default in 3.18

Postby DrTeeth » Thu May 31, 2018 10:45 am

On Tue, 29 May 2018 13:43:58 EDT, just as I was about to take a herb,
Bob Coleman disturbed my reverie and wrote:

>When you create a full backup and then a changes only backup using the full as the base, the result is either a differential or incremental depending on how it is subsequently used or not used.

AIUI, it is always a differential and not affected in the slightest by
subsequent incrementals.
--
Cheers,

DrT

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with democracy, spend five minutes with
the average voter." - Winston Churchill
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Re: Create Sector Hash Files default in 3.18

Postby DrTeeth » Thu May 31, 2018 10:52 am

On Wed, 30 May 2018 17:46:06 EDT, just as I was about to take a herb,
Bob Coleman disturbed my reverie and wrote:

>For whatever it's worth, I create a full backup once a week and an incremental on each of the following six days. So far, I've never had a problem picking any incremental and restoring from it.

I concur. I have a base full backup and two folders off that. When the
screen in IfW gets full, I swap to the other folder and after a few
days, delete the contents of the other folder. I also backup to an
external drive.

The only issue I had with incremental backups is that they were not
included with IfW as the programmer deemed them to be too risky...then
they appeared.
--
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DrT

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with democracy, spend five minutes with
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Re: Create Sector Hash Files default in 3.18

Postby Bob Coleman » Fri Jun 01, 2018 11:51 am

DrTeeth wrote:
> On Tue, 29 May 2018 13:43:58 EDT, just as I was about to take a herb,
> Bob Coleman disturbed my reverie and wrote:
>
> >When you create a full backup and then a changes only backup using the
> full as the base, the result is either a differential or incremental
> depending on how it is subsequently used or not used.
>
> AIUI, it is always a differential and not affected in the slightest by
> subsequent incrementals.
> --
> Cheers,
>
> DrT
>
So you are saying that the first one is always a differential and then anything based on that is an incremental? I guess that makes sense.
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Re: Create Sector Hash Files default in 3.18

Postby TeraByte Support(PP) » Fri Jun 01, 2018 12:15 pm

Each "Changes Only" backup is a differential based on the image selected as the base. The base image could be a full or it could be a differential/incremental.

In the case of incrementals, they are usually called that when they are a chain of backups, each backup depends on the previous one. In the case of differentials, each backup usually only depends on one other backup (the full base image).

Full 1
* Differential 1 (based on Full 1)
* Differential 2 (based on Full 1)
* Differential 3 (based on Full 1)

Full 2
* Incremental 1 (based on Full 2)
* Incremental 2 (based on Incremental 1)
* Incremental 3 (based on Incremental 2)

The first Changes Only backup is exactly the same regardless of whether you think of it as a differential or an incremental. For example, Incremental 1 is also a differential. Or, you could later make a new backup based on Differential 1 and then consider Differential 1 as an incremental.
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