Synthetic full backup - Actual consumption on Storage !!

Question

I did really like the new Synthetic backup , I read about it and tried to simulate the situation

Synthetic full backup for NetWorker 8-Testing PII | Ahmad Sabry ElGendi

Everything goes fine as documentation , but I have 2 concerns / questions confusing me:

1- Why storage gets more space as I am going to perform more synthetic Full or incremental ?

in other words , When I perform 100 MB full , then 10 MB incr, then another Full , the size as per my understanding should be 110MB but no more , but I believe it gets more than this a lot on storage , so what is the point of it then ?

2- If I did synthetic :

Saturday: 2 PM Full 100 MB

Sunday: 2 PM incr 10 MB

Monday: 9 am deleted 20 MB data

2 PM incr 10 MB

Tuesday: 2 PM incr 10 MB

Wednesday: 2 PM incr 10 MB

Thursday: 2 PM incr 10 MB

Friday: 2 PM incr 10 MB

3 PM Full

how much data will be @ Friday 3 PM ?

180 MB ?

or

140 MB ?

I believe the size:

- on client Disk will be 140 MB ,

- on Backup storage should not lose the 20 MB deleted on Monday as they might be required to be restored as of Sunday data !!

- After Full Backup Job should show 140 MB

Any idea ?

Thank you

Message was edited by: ahmadelgendi

ble1 · Accepted Answer

ahmadelgendi wrote:

Please remove first line , it might be exposing NW exam , and really I am not here to talk about this at all

I didnt really get how did you explain it to me , let us say ,, it is static change increasing every day ,, one day there was data removed after the increased , in other simple words ,, the next Full ,, will hold the removed data or not ?,, because what if some user wanted to restore data prior to deletion 9 am Monday , so the last Saturday Full + Sunday Incr. will hold it , I am afraid my english is not much good ,, but I am sure you understand me ,, will the Firday 3 PM Full Backup will incldue the removed data from Monday ? or the size will not be the same ,, I am really confused !!

Don't worry, question is enough different not to be relevant to exam. Let's try this way. First, I suspect that your Friday is not full, but synth incremental level, right? So, we have:

Day	Level	Change	Restore
Saturday	full	100MB	100MB
Sunday	incr	10MB	110MB (full + incr)
Monday	incr	10MB	120MB (full + 2x incr)
Tuesday	incr	10MB	130MB (full + 3x incr)
Wednesday	incr	10MB	140MB (full + 4x incr)
Thursday	incr	10MB	150MB (full + 5x incr)
Friday	incr	10MB	160MB (full + 5x incr)

Now, let's introduce synthetic full.

Day	Level	Change	Restore
Friday 3pm	incr_synth_full		100MB

Now, above is not entirely correct, but it will be more clear with following explanation:

If change column reflects changes of the same files, then all these files will be in consolidated save set and their size we can't estimate as many times files in incremental do not change in size, but some other property like changed time timestamps which does not reflect necessary size of the file itself
if size has changed, or any other property of the file, then always latest version of the file. For example, if myfile.bat has changed on Monday, Wednesday and Friday 2pm, then 3pm synth version will contain only Friday 2pm version.
The fact that you deleted some files does not matter as synth incremental merges full and all subsequent incrementals into "new full" containing original full updated with latest version of changed files since. So, this means that your removed data will be included.

Example: Save set G: has two files called fileA and fileB:

Day	Level	Change	Content
Saturday	full		FileA and FileB
Sunday	incr	FileA	FileA
Monday	incr	FileC, FileB	FileC, FileB
Tuesday	incr	FileB	FileB
Wednesday	incr	FileA	FileA
Thursday	incr	FileA removed FileC	FileA
Friday 2pm	incr	FileB	FileB
Friday 3pm	incr_synth_full		FileA from Thu, FileB from Fri 2pm and FileC from Monday

bingo.1 · Answer

With these data you will never be able to say as you have no idea whether you backup the same files or other files.

Worst case it could be up to 160MB (1x100MB + 6x10MB) as NW will only use the backups.

However, a true full could of course only backup what the client actually uses.

ble1 · Answer

Interesting enough, similar question is part of NW certification

Your question was how much data there will be on Friday 3pm and based on what you said the answer is 80GB. Why? You do not say if data is added or not so we assume static. You do say that 20GB is removed and since on Friday at 3pm you run full (see your initial post) level that means you will have same amount of data as last full minus removed data (note that incremental size may be due to change of file only).

With that in mind, and fact that you asked virtual synth, I assume this is not what you wanted to ask so what exactly did you wanted to know?

AhmadElGendi · Answer

I believe there should be 3 different sizes:

1- On client disk , = Full + all Incr - removed data

2- On NW Storage = Full + all Incr + removed data (I mean here the total savesets will include the removed data but the Full Backup will be as N#3 below).

3- On Friday Full Backup = Full + all Incr - removed data ,, Same as N# 1

Correct ?

AhmadElGendi · Answer

Please remove first line , it might be exposing NW exam , and really I am not here to talk about this at all

I didnt really get how did you explain it to me , let us say ,, it is static change increasing every day ,, one day there was data removed after the increased , in other simple words ,, the next Full ,, will hold the removed data or not ?,, because what if some user wanted to restore data prior to deletion 9 am Monday , so the last Saturday Full + Sunday Incr. will hold it , I am afraid my english is not much good ,, but I am sure you understand me ,, will the Firday 3 PM Full Backup will incldue the removed data from Monday ? or the size will not be the same ,, I am really confused !!

ble1 · Answer

Made a typo.. there is synth_full and incr_synth_full so in essence I was referring to synth_full (difference is that incr_synth_full would perform incr and then full).

AhmadElGendi · Answer

Clear enough , Thanks a lot for your time

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Synthetic full backup - Actual consumption on Storage !!

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