Need some help with the media pool policies

[sub2o5]

Hello,

as the topic tells: I need some help as i'm quite new to the topic of tape backups.

We have a PBS saving around 8TB of machines (last snapshot) per day.
Our media pool should have 4-5 friday/weekend-tapes (full) and 4 weektime tapes for incremential changes to keep the duration low.

Right now, i configured the pool to alway allocate and 7 days retention.
That's obviously wrong as every tape seems to get all data.

I should set allocate to friday evening, correct?

As we do not have a changer, how need holidays to be handled?
F.e. if friday is a holiday (nobody will change the tape then) - can we just put in the friday-tape on thursday?
When having multiple friday-tapes, this one would get overwritten on thursday already, because it's already over 7 days old.
Or would it used as a full-backup on thursday AND get the incremential changes on friday automatically?

As u see, i'm quite a bit unsure about the terms and concepts used here and need some advice.

Kind regards
Stephan

 

[dcsapak]

did you see the tape docs already? it probably clarifies some points up-front:
https://pbs.proxmox.com/docs/tape-backup.html

in pbs, tape backup does not do full / incremental updates, each media-set contains all data necessary to restore and the data is deduplicated, so you can include more snapshots on less tapes

the real question is: for how long do you want to keep your snapshots, and on how many copies do you want it to have?
if you just want a media-set per week you must set the allocation to once a week, and retention to however long you want to keep those media-sets (e.g. 4 weeks)

 

[sub2o5]

I already keep snapshots of everything on 2 separate systems (one on-site, one synced to my location) - the tape backup is just the last resort and should only contain the most recent snapshot of each vm ("last only" - works as expected)

I also read trough the documentation, but some parts are - unfortunately - not 100% clear to me.

Isn't it possible to to a backup of all snapshots (last only) once a weekend and just write the differences (relative to the weekend!) of every snapshot out on every weekday?

 

[dcsapak]

Isn't it possible to to a backup of all snapshots (last only) once a weekend and just write the differences (relative to the weekend!) of every snapshot out on every weekday?

what do you exactly mean by this?

if snapshots get added to a media-set, first the chunks have to be written to it. these chunks are deduplicated by media-set, so a chunk is not written twice. if you backup your snapshots every day (on the same media-set), the first one will write all chunks for those snapshots on the tape, and the subsequent jobs will add the new chunks + snapshots (so exactly what you want?)

if a new media-set starts (by using the 'allocation policy'), the chunks have to be written again since the new media-set does not contain any chunks (yet).

 

[sub2o5]

Yes, that's exactly what i want!

Currently my pool hat "allocate always" and "retention 7 days" - which isn't what i want.
Setting it to "allocate fr. 17:00" and "retention 7 days" while running the jobs mo-fr 18:00 would result in a new set every friday evening, starting with ALL chunks of the last snapshots on the friday-tape and only the new chunks on the next mo-th-tapes?
Just wanted to clarify if my thoughts are correct here.

 

[dcsapak]

yes it should work that way

 

[sub2o5]

Great. Thanks a lot.

Is there an elegant way to handle holidays? So inserting the Friday-tape at thursday f.e. will not work if we use several friday-tapes for the month - or will the Friday-tape get written to on thurday _AND_ friday with the new allocation policy?

 

[dcsapak]

when you create a tape backup job, the list should show the next 'expected' tape (that is, when the configuration does not change in the meantime, and there is enough space)

if you have retention on, it will not overwrite the media-set immediatly, but keep it for the amount of time you specified. (e.g. 7 days retention means it keeps the media-set 7 days *after* starting a new one)