BE 12.5 et Protection contre l'écrasement

[Fcorvaisier]

Bonjour,

J'utilise aujourd'hui BE avec deux jeux de cassettes par jour.

Si comprends bien le principe de la protection contre l'écrasement c'est que toute la cassette est protégée, il n'y a pas de distinction entre la sauvegarde de la veille et celle d'il y a deux semaines.

Donc si je veux utiliser une cassette toutes les deux semaines il faut protéger cette cassette contre l'écrasement à 2 semaines moins 1 jour.

Mes questions sont donc :

- Une fois qu'il est arrivé au terme de l'espace disque disponible va-t-il forcément ré-écrire sur les données les plus anciennes et garder une cohérence dans les sauvegardes existantes ?

- Comment je peux être sûr d'avoir une rétention de 8 semaines, est-ce que cela ne dépend seulement de la taille des données que je lui sauvegarde ou y a-t-il un autre paramètre à configurer ?



Par exemple si je sais que j'ai 250 Go à sauvegarder chaque semaine sur deux cassettes (2T chacune) alors je peux sauvegarder 16 semaines dessus.
Le problème est que si ma volumétrie augmente je ne pourrais plus tenir les 16 semaines et il écrasera les premières données sans me le dire alors que j'aurai pu ajouter une cassette pour pouvoir tenir mes 16 semaines. Parce que pour moi la durée de retention est plus importante que le nombre de cassette.


Merci d'avance.


François

[pkh]

I am using Google translate to understand your question, so my understanding may not be perfect.

BE protect data from being overwritten by using the Overwrite Protection Period parameter of the backup media set.  The amount of data on the media does not matter.  If you are using a tape and it is full, BE will use the next available overwriteable tape in the tape library or prompt you to put in an overwriteable tape.  If you are backing up to disk, BE will pause the job when the Low disk space threshold is exceed until you free up enough space for it to continue.

[Fcorvaisier]

Thank you for the time you take.

I'll try to translate my post as your answer is near.

My questions are :

 - Does BE rewrite automatically on the first data when my media is full, and will it keep coherence in the catalog. I suppose here that the data protection is not set.
 - How may I be sure that I have 8 weeks of retention ?

Exemple :

I have 250G to save on 2 tapes OF 1T.
The tapes turns every weeks, so I could Save on 1 tape for 8 weeks before one tape is full.
There I know by calcul that my retention is 8 weeks.

But now the size of data to backup is not always the same or will growth, so on One tape i'll not be able to save 8 weeks, but perhaps 7.

How i can say to BE that i want to keep my backups (not tapes) for 8 weeks, and i don't care to add one or more tape, all i want is to preserves my backup for 8 weeks.

I hope that i was clear ?


François

[pkh]

If you set your OPP (overwrite protection period) to 8 weeks, then your data will be protected for 8 weeks from the time the job that backed them up ends.  It does not matter which tape(s) they are on.

Your situation is slightly tricky because you are appending your data.  When you append data, the OPP starts from the time the last backup job ends.  In your example, after your Week 1 job runs, the tape is protected until week 8.  When your Week 2 job appends data to the tape, then the tape is protected for a further 8 weeks, i.e, it is write protected until week 9.  When your Week 3 job appends data to the tape, the tape is protected for a further 8 weeks, i.e., it is write protected until week 10, and so on.  After your Week 8 job ends, the tape is protected until week 15.  You can only re-use the tape after week 15.  From this example, you can see that your week 8 data is protected for 8 weeks, but your week 1 data is actually protected for 15 weeks. 

[Fcorvaisier]

Thank you,

So I understand well the way it works, but i wonder how I can set protection over the data and not the tape.

If my tape is a 1T tape, and i didn"t mention the OPP, and every week I backup 250 G how does it will manage to rewrite on my tape when it will be full ?
Will it keep the catalog fine ?
will he always write on the oldest data on that tape ?

[pkh]

The OPP is protecting your data by preventing the tape from being overwritten.  As I said, your case is tricky because you are appending to the tape.  If your job overwrite the tape, then each tape will be protected from being overwritten for 8 weeks and your data in it will be safe for 8 weeks.

 I didn"t mention the OPP

There is always an OPP setting. You cannot avoid it.

When the tape become recycleable, i.e. the OPP has expired, then you job can overwrite it.  When a tape is overwritten, all the previous data on the tape is gone.  In your example, you have 8 weeks or 2TB of data on your tape, then you would loose all these when the tape is overwritten.

By the way, what tape device are you using?  I am not aware of any tape that can hold 2TB of data.

[Fcorvaisier]

Ok, thank you.

I think i have my answer.
;)

My tape is LTO Ultrium 4 from Dell, it's said as 1.6 T when compressed, but most of the time I can got to 2T.

And about the Catalog, it will keep the data as long as the tape is not overwritable ? Or when the data is overwritten ?

I would say as long as the tape is protected, but i would prefer a confirmation.


Thank you.

François

[pkh · Accepted solution]

My tape is LTO Ultrium 4 from Dell, it's said as 1.6 T when compressed, but most of the time I can got to 2T.

You are lucky that you got such good compression ratio, but your compression ratio can very easily decrease when the types of files that you are backing up changes.
 

And about the Catalog, it will keep the data as long as the tape is not overwritable ? Or when the data is overwritten ?

As long as the tape is not overwritten, information regarding the data that is on the tape will remain in the catalog.  Once it is overwritten, only information regarding the new data will be in the catalog.  The old one will be purged.

If you are happy with the answers, do close out this discussion by marking one of my answers as the solution.

[Fcorvaisier]

Ok.

Thank you for your responses.

I got all I wanted.