bloomer1176 Posted April 2, 2003 Report Share Posted April 2, 2003 I was just wondering how the backup process works. I am in a school where most of the computers have the same set of apps and programs. I was told that if one computer gets backed up with lets say MS Word that when it hits another computer that has Word it will not need to back it up because it would use the previous computers Word backup.. If it needs it later for a restore it will take the one from the other source. I was under the impression that each computer is backed up the first time then only modified files. I notice that my clients backups the first time are very large then smaller and smaller. Just hope someone can clear this up for me. Thank you Eric Seaford Schools NY Link to comment Share on other sites More sharing options...
mcswgn Posted April 3, 2003 Report Share Posted April 3, 2003 That is all correct. Every time a client is backed up, Retrospect takes a "snapshot" of the current configuration. It then matches the files in the snapshot against the files it already has in its catalog (both from previous backups of this client and other clients). If it doesn't need to write the file to the backup media because it's already there, then it won't. What I don't know is exactly how Retrospect decides that two files are the same, although it seems to be pretty conservative (which is good). For example, a changed modification date will be enough to trigger a file to be backed up again. Link to comment Share on other sites More sharing options...
AmyJ Posted April 3, 2003 Report Share Posted April 3, 2003 Quote: What I don't know is exactly how Retrospect decides that two files are the same, although it seems to be pretty conservative (which is good). For example, a changed modification date will be enough to trigger a file to be backed up again. Retrospect uses several matching criteria to find new or changed files. If one of the criteria has been changed, Retrospect will back up the file again. On Windows, Retrospect looks at creation date and time, modified date and time, size and name. If match only in same location option is set, Retrospect matches on the path, volume name and drive letter also. By default, the archive attribute is not used as a matching criteria in Windows, allowing for true and reliable backups to multiple backup sets. On a Mac, Retrospect looks at name, size, type, creator, creation date and time, modify date and time, and label. Link to comment Share on other sites More sharing options...
bloomer1176 Posted April 9, 2003 Author Report Share Posted April 9, 2003 Thank you, I just want to clear something up, so I understand this. If my first client has Word for OS X then my 50th client who has the same Word for OS X will not back that up because the program knows it has the app from a previous source. I ask this because all of my OS X clients first backups were huge, seemed like it backed up everything. I also ask this because the way an App is setup on one computer could be different then how it is on another. also when you mention snapshot, is it comparing the snapshot to itself each time or checking to see if the app is somewhere else. If this is the case couldn't you shorten the time it takes to backup a lot of computers by having the one with the most apps and programs first on the list this way when it hits other computers it's just backing up files. I ask these questions because I am trying to fine tune my backup plan. The list of clients is growing and I want to find the best solution. thank you again. Eric Bloomfield Link to comment Share on other sites More sharing options...
mcswgn Posted April 9, 2003 Report Share Posted April 9, 2003 Quote: If my first client has Word for OS X then my 50th client who has the same Word for OS X will not back that up because the program knows it has the app from a previous source. Yes. as long as the "name, size, type, creator, creation date and time, modify date and time, and label" are the same, the file will not be rewritten. That does not mean, however, that nothing you think of as being the same won't be rewritten. For example, if one user likes to "label" all of his/her applications so they list in a particular order (when sorted by label) and nobody else bothers to do anything like that, then this individual will always have their applications all written to tape no matter how many copies of the same version are out there on the other clients. Just to give an example. I just started a "recycle" backup, so all clients are being backed up from scratch. One of my clients just finished the matching phase on its first backup to the new set. It is not the first client to get backed up to this set; there have been several other MacOS X clients (at the same OS version) that have already been backed up and against which this client can be matched. This client has about 5.6GB on its disk and the backup window is saying that 2.4GB need to be written to the backup set. So that means 3.2GB was successfully matched against files on other clients and so didn't need to be written again. In spite of that, if I later come back to look at this "snapshot" (the complete record of the status of this client as of this date and time), it will show me all 5.6GB of files. Quote: couldn't you shorten the time it takes to backup a lot of computers by having the one with the most apps and programs first on the list this way when it hits other computers it's just backing up files. It doesn't matter the order. The first time that file/app is hit, it will be backed up. After that, if it is successfully matched against another copy, it won't be backed up again. No matter which of these clients comes up first, the file is still written once and takes the same amount of time. Link to comment Share on other sites More sharing options...
Lennart_T Posted September 5, 2003 Report Share Posted September 5, 2003 Quote: mcswgn said: Quote: couldn't you shorten the time it takes to backup a lot of computers by having the one with the most apps and programs first on the list this way when it hits other computers it's just backing up files. It doesn't matter the order. The first time that file/app is hit, it will be backed up. After that, if it is successfully matched against another copy, it won't be backed up again. No matter which of these clients comes up first, the file is still written once and takes the same amount of time. It would help if you had a HUGE local disk on the backup computer with "everything" loaded onto it and back up that disk first. Then Retrospect wouldn't have to pull so many files over the network. Link to comment Share on other sites More sharing options...
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