Hello, pon., 6 wrz 2021 o 20:21 <neumei...@mail.de> napisał(a):
> But I'm quiet sure that I do understand the behaviors of them. However In > case I did get something wrong I will write out > the behaviors and would acknowledge if someone could point out if I should > got something wrong. Thank you. > > For a given job: > -an incremental backup references the most recent backup of any > kind(incremental,differential,full) and backups all the data that changed > since then > -a differential backup references the most recent differential or full > backup and backups all the data that changed since then > No, any differential backup refers to the recent full backup only. So it backup all changes from full and basically every subsequent differential backup "includes" all changes available in previous differential backups. The idea behind differential levels is that you need a single differential in the restore chain to optimize the restore procedure. > -a full backup references nothing and backups all the data > > > You have got me right. You wrote: "If you are doing a "daily" and a > "weekly" incremental of the same job, > then the "weekly" either isn't really "weekly" or isn't really > incremental." > That's exactly what I was attempting to do. My goal was to shrink the > space all my backups need by introducing a second > incremental-pool with a longer retention period, but this leads straight > to the problem you have described under the > "Now what you COULD do, ..."-paragraph that I am trying to avoid. I'm > Sorry that I didn't made it clearer. > Thank you for pointing out the Virtual Full option. I didn't know about > that. > Differential backups are not designed to optimize for "space". They are designed to optimize restore procedures. Just take a look for an example backup levels policy: - Full once a month - Differential once a week - Incremental every day In this case if you need to restore the whole month of data from backup then you will need a single Full + a single (third) Diff and a few (up to six) Incrementals. On the other hand the "standard" Full + every day incrementals without intermediate diffs requires a single Full + about 30 Incrementals. > There just popped up another question in my head: > - should I preferably use the Virtual Full option to make full backups or > the normal full backup-option? Are there any downsides? > The virtual full option is the right solution in most cases if you have resources to implement it. For example it requires no less than 2 archive devices defined in Storage Daemon, so if you have a single tape drive it simply won't work. I hope it helps. -- Radosław Korzeniewski rados...@korzeniewski.net
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