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pshute
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Incremental to Reverse Incremental - disk space requirements

Post by pshute » Jun 21, 2017 10:30 pm

We currently do an incremental backup each weekday, with an active full backup once a week, and are keeping 10 restore points. That gives us access to daily backups for the last two weeks.

We'd like to keep more restore points, but don't have the disk space, so we're thinking of changing to Reverse Incremental. I'd like to know:
- how many more restore points that will let us have
- what happens to future active full backups
- what happens to existing full backups
- what will be the impact on disk space during the first two weeks

At the moment we have these files in the repository:
07/06/2017 05:18 AM 1,518,283,966,464 Backup Job 1 - mainD2017-06-06T210114.vbk
08/06/2017 12:59 AM 67,000,223,744 Backup Job 1 - mainD2017-06-07T210144.vib
09/06/2017 12:47 AM 73,356,963,840 Backup Job 1 - mainD2017-06-08T210115.vib
10/06/2017 12:38 AM 70,295,049,216 Backup Job 1 - mainD2017-06-09T210117.vib
13/06/2017 12:36 AM 74,783,447,552 Backup Job 1 - mainD2017-06-12T210057.vib
14/06/2017 05:08 AM 1,515,549,227,520 Backup Job 1 - mainD2017-06-13T210103.vbk
15/06/2017 12:41 AM 75,472,141,824 Backup Job 1 - mainD2017-06-14T210100.vib
16/06/2017 12:44 AM 82,936,717,312 Backup Job 1 - mainD2017-06-15T210104.vib
17/06/2017 12:42 AM 73,508,951,552 Backup Job 1 - mainD2017-06-16T210056.vib
20/06/2017 12:52 AM 90,038,958,080 Backup Job 1 - mainD2017-06-19T210058.vib
21/06/2017 06:17 AM 1,541,633,617,920 Backup Job 1 - mainD2017-06-20T210103.vbk
22/06/2017 12:47 AM 70,325,822,464 Backup Job 1 - mainD2017-06-21T210222.vib

You can see we have three full backups of about 1.5TB in there, and 9 incrementals averaging about 80GB. I assume it's keeping 11 files because the 4 oldest incrementals need the oldest full, and that tomorrow there will be 12 files, then 13, etc, until it finally removes the oldest active full and all its incrementals.

If I reconfigure the backup to Reverse Incremental, will it immediately convert the latest incremental to a full, and all the previous files to reverse incrementals? Or does nothing happen till after the next backup? If the latter, does it convert all the files, or only the backups done snce the change?

And what happens to future active full backups? Do they still get converted to reverse incrementals after the next backup?

At the moment, the main reason for doing weekly active full backups is so that we can then back it up on tape the next day. I assume with Reverse Incrementals, we could do them much less often, and that they are perhaps not even necessary. Correct?

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Re: Incremental to Reverse Incremental - disk space requirem

Post by pshute » Jun 21, 2017 11:04 pm 1 person likes this post

Is this simulation an accurate reflection of how Veeam Reverse Incrementals work?
http://rps.dewin.me/

If so then it looks like active fulls are retained even when using Reverse Incrementals, so in order to save space, we have to either stop doing them, or do them less often.

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Re: Incremental to Reverse Incremental - disk space requirem

Post by skrause » Jun 23, 2017 1:13 pm

Unless you absolutely need every restore to be from a full, using Forever Incremental with periodic health checks is the recommended backup type. You get the same disk space usage as Reverse Incremental but the I/O penalties are lower and the snapshot only stays open long enough for the changes to be backed up as the merge operations happen after the data backup portion is complete.
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pshute
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Re: Incremental to Reverse Incremental - disk space requirem

Post by pshute » Jun 23, 2017 2:17 pm

The reason we've been considering reverse incremental is that we back up to tape weekly, and it saves space on the tape, and backup time, to only back up the most recent full backup, so it's best if that full is very recent. If we do forever incremental then the most recent full is always a week old. Correct?

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Re: Incremental to Reverse Incremental - disk space requirem

Post by skrause » Jun 23, 2017 2:26 pm

No, With tape it will create a "virtual synthetic full" from the most recent restore point.

https://helpcenter.veeam.com/docs/backu ... tml?ver=95
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Re: Incremental to Reverse Incremental - disk space requirem

Post by pshute » Jun 23, 2017 7:58 pm

Thanks, I didn't know that. I don't understand the tape diagram on that page though. It shows two fulls and several incrementals on the tape.

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Re: Incremental to Reverse Incremental - disk space requirem

Post by pshute » Jun 28, 2017 9:26 pm

skrause wrote:Unless you absolutely need every restore to be from a full, using Forever Incremental with periodic health checks is the recommended backup type.
Can you please tell me where this is recommended? We've been doing regular active full backups based on the advice I received in this thread:
vmware-vsphere-f24/synthetic-backup-or- ... ml#p169619
In addition to the info above you should keep in mind that when doing the synthetic full, Veeam uses the chain of incremental to build the full backup. Imagine one of the restore points has corrupt data thus your synthetic full might be unusable. That is why you should consider doing a periodic Active Full.
Perhaps enabling the health checks guards against that problem?

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Re: Incremental to Reverse Incremental - disk space requirem

Post by skrause » Jun 28, 2017 9:48 pm

Ever since they added forever forward Veeam have been recommending using the method compared to reverse incremental.

Using it compared to running active fulls with a forward incremental chain is always dependent on a number of factors.
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Re: Incremental to Reverse Incremental - disk space requirem

Post by pshute » Jun 28, 2017 9:50 pm

Recommended over reverse incremental I can understand. I'm not comfortable going against the advice in the thread I quoted though.

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Re: Incremental to Reverse Incremental - disk space requirem

Post by sistema » Apr 18, 2019 1:38 pm

skrause wrote:
Jun 23, 2017 2:26 pm
No, With tape it will create a "virtual synthetic full" from the most recent restore point.

https://helpcenter.veeam.com/docs/backu ... tml?ver=95
But with reverse incremental, when i do a backup to tape, it saves backup time becouse it have not to create a full, right?
Thank you

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Re: Incremental to Reverse Incremental - disk space requirements

Post by veremin » Apr 18, 2019 3:23 pm

In terms of amount of data copied to tape both modes will be similar, however, you're right in saying that synthetic activity caused by virtual full creation might result in increased backup duration. Thanks!

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