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Normal Backup with Multiple Disk Media Sets

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So I am trying to understand how using multiple disk media sets with a normal backup script will work.


I have setup two disk media sets, A and B.

I have created a backup script that has a schedule to backup to media set A on M, W, F. The same script that has another schedule to backup to media set B on T, Th, Sat.

So what I am looking to figure out is if the backup script is striping the data across both media sets? Or is it simply copying all of the same data to both media sets on a rotating bases?


The reason I ask is that the source volume is larger than the destination media sets. So, I would like to stripe the backups across both media sets to accommodate for the size difference. If the above scenario is not appropriate for this, how should I do it instead?




Screen Shot 2018-01-03 at 3.33.04 PM.png

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It all depends on what your backup objective is, Macspt

If your objective is to maintain a single comprehensive backup of your source volume, then you should have a single disk Media Set rather than two—with your two backup disks as the two Members of that Media Set.  To understand why using two separate Media Sets will not result in "striping", read the third paragraph after the bolded paragraph in this section of the old version of the Wikipedia article.  That section—because it refers to Retrospect Mac 6 and previous versions as well as Retrospect Windows—uses the term Backup Set instead of Media Set, but  it is still the case that "Retrospect maintains a separate Catalog File—distinct from any OS-maintained directory—on disk for each [my emphasis] Backup Set."  So when you asked "is it simply copying all of the same data to both Media Sets on a rotating bases?", the answer is yes.  Besides, if "striping" was actually being done and you wanted to restore a particular daily version of a rapidly-changing document, how would you know which Media Set to use unless you knew which day of the week the version had been backed up?

If OTOH your objective is to maintain two comprehensive backups that are the same except for the most recent day, so that you can keep the least-recent backup off-site, then you'll have to buy an additional backup disk with a capacity as big as the two you already have.  This may not be as big a financial burden as you think; large-capacity disk drives are getting cheaper each month.  For carrying off-site  the Media Set that has as its two Members the backup disks you already own, I suggest buying a cheap chest-pack camera bag—as I did for carrying  on the bus the disk drive I took home weekly at my last job.

Edited by DavidHertzberg
Clarified third sentence of second (first multi-sentence) prgf.
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It was exactly what I was looking for, and I have modified the Disk Set so that it includes both Hard Drives as members for a total backup storage of 13.7TB. This should allow me to backup the primary 8TB storage array for a couple months before I have to recycle the backup set.

Thanks for the info, it was very helpful.

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A quick look at your past posts makes it appear that you may not be familiar with the capabilities of recent versions of Retrospect, so I am wondering whether you are aware of the enhancements to the Grooming feature that were added to Retrospect Mac 12 and 13.  I mentioned them in the first paragraph and the P.P.P.S. of this post in another thread

With the "new grooming option [that] allows you to determine the number of months of backups to keep" , you might not need to recycle your 13.7TB Media Set at all.  That assumes that your installation is saving some kind of text documents, so that you don't necessarily need to save every version of them in order to satisfy regulatory authorities.  If OTOH your installation is saving video or audio documents, where every version may be important, Grooming would not be appropriate.  In fact another client-server backup app, whose developers at one point attempted to compete with Retrospect but decided around 2009 to concentrate on a "desktop archival and recovery application designed specifically for the Music, Film, and Television production environment", AFAICT never developed a Grooming feature.  That app, which I'll refer to here as TB, still emphasizes its capabilities for backing up to tape—which of course cannot be Groomed; I'll assume your installation is not that kind of environment, since your Media Set consists of disks.


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