locked
Need more detail on backups RRS feed

  • Question

  • Can someone explain in detail what WHS is backing up at each interval? What is the difference between a monthly, weekly and daily backup? They can't all be incrementals from the day before??
    Saturday, September 5, 2009 10:21 PM

Answers

  • As long as a cluster stored in the database is "used" by even a single backup in the database (no matter what computer that backup was from) it will be retained. So for every backup shown in the console, for any backed up computer, all clusters are available (and in most cases, almost all are shared between multiple backups and even multiple computers). Anything else would be egregiously stupid on Microsoft's part. I think the technical brief I linked actually mentions that... (Not the egregiously stupid bit. :) )

    Does that help?
    I'm not on the WHS team, I just post a lot. :)
    • Marked as answer by CSWG Wednesday, September 16, 2009 2:34 AM
    Sunday, September 6, 2009 3:27 PM
    Moderator

All replies

  • Can someone explain in detail what WHS is backing up at each interval? What is the difference between a monthly, weekly and daily backup? They can't all be incrementals from the day before??

    They are all the same.  Each backup is a "full backup".  However, if a cluster has already been backed up, it won't backup the cluster again.  It will create a "tombstone" which points to the real cluster instead (thereby saving space).  As for the daily/weekly/monthly, it's strictly a retention policy.
    Saturday, September 5, 2009 11:32 PM
    Moderator
  • Ok, here's a simple scenario. Fresh install of OS on workstation. WHS performs first, full backup. Next day one file changes. Next night WHS backs up the one file. This file never changes again. Four months later you need to restore this file. Default policies will have erased every backup set (except the first one I assume) while continuing to make new ones. Is this file gone?

    Sunday, September 6, 2009 1:16 AM
  • Another way of asking the same question is, I thought that you cannot erase even a single incremental backup set without the risk of losing a file that was changed right before that backup, but not since, as it won't exist on any further backups?

    Unless WHS is performing differentials every time, but what you describe are incrementals.
    Sunday, September 6, 2009 1:22 AM
  • As far as the end user is concerned, Windows Home Server performs a full backup every night. Conceptually, it functions in a fashion similar to incremental backups, in that it attempts to minimize the amount of data actually backed up each night. But the traditional terms: full, differential and incremental are not truly applicable to Windows Home Server's backup engine.

    Internally it uses a concept similar to single instance storage, only at the data cluster level, to ensure maximum efficiency of disk and network utilization for backups. The result is that the very first time a used cluster of data from a partition is backed up, the actual data is sent and stored in the backup database. From that point on, any time any client computer attempts to back up a cluster with identical data no actual data needs to be transmitted. Instead, that backup set on the server just gets a pointer to the data already in the database.

    You can learn more about the Windows Home Server backup engine in the Home Computer Backup and Restore technical brief.
    I'm not on the WHS team, I just post a lot. :)
    Sunday, September 6, 2009 4:04 AM
    Moderator
  • kariya21 and Ken, thanks for the info, but I still can't quite get my head around it.

    If we assume I only have one workstation and performed standard incremental backups to a tape drive, I wouldn't have any redundant data backed up, just like WHS, but I would not be able to delete even one of the sets without risk of losing data.
    Unless WHS doesn't just blindly delete everything in a backup set when it expires and instead selectively deletes only those clusters that have since changed from when the backup was run, and therefore are no longer valid, I still can't see how this works.
    My best description, based on what I've read, would be that the daily, incremental backups, are "merged" (entered into the database) with the first, full backup while keeping the old, outdated records intact. Those old records are then purged when their particular backup set expires, while valid records from that same set DO NOT get erased. So if I choose to delete a backup set from last week, I might assume it's obeying my command and deleting everything from that set, but it's really only deleting the old, outdated records and refusing to delete valid stuff.
    Am I close? Any documents that are less, um, brief? ;-)
    I don't mean to be annoying, it's just I take backing up seriously and need to understand what WHS is doing so I can better manage my backups. I really appreciate the replies.
    Sunday, September 6, 2009 2:43 PM
  • As long as a cluster stored in the database is "used" by even a single backup in the database (no matter what computer that backup was from) it will be retained. So for every backup shown in the console, for any backed up computer, all clusters are available (and in most cases, almost all are shared between multiple backups and even multiple computers). Anything else would be egregiously stupid on Microsoft's part. I think the technical brief I linked actually mentions that... (Not the egregiously stupid bit. :) )

    Does that help?
    I'm not on the WHS team, I just post a lot. :)
    • Marked as answer by CSWG Wednesday, September 16, 2009 2:34 AM
    Sunday, September 6, 2009 3:27 PM
    Moderator
  • As long as a cluster stored in the database is "used" by even a single backup in the database (no matter what computer that backup was from) it will be retained.
    But WHS deletes backups on a schedule. If a file is backed up tonight and never changed again, and six months later you need it, WHS will have deleted backups every 3days/3weeks/3months so, based on what you said the file should be gone. Unless...
    When the set that held that backup was pruned, WHS rediscovered that those clusters were used during the next backup and added those clusters back into the database, and when that set gets erased they will be re-added again and so on.
    In that case I would hope WHS would be smart enough to simply check the expired sets before erasing them to determine if there are still used clusters involved and simply not erase those clusters.
    Or maybe WHS refreshes the dates of every used cluster, in the database every time it runs a backup. Changed clusters will be added and their old records will then be left with the old dates and only those get erased via pruning.

    These are the gory details I seek. ;-)
    Sunday, September 6, 2009 10:03 PM
  • But WHS deletes backups on a schedule. If a file is backed up tonight and never changed again, and six months later you need it, WHS will have deleted backups every 3days/3weeks/3months so, based on what you said the file should be gone.

    Only if you never backed up any computer that needed that cluster in the last 3 months.  Remember, the "full backups" occur nightly so that cluster will be needed for tonight's backup, tomorrow night's backup, the following night's backup, etc.

    Unless...
    When the set that held that backup was pruned, WHS rediscovered that those clusters were used during the next backup and added those clusters back into the database, and when that set gets erased they will be re-added again and so on.
    In that case I would hope WHS would be smart enough to simply check the expired sets before erasing them to determine if there are still used clusters involved and simply not erase those clusters.

    It knows what clusters to keep and what to get rid of (based on the retention policy you set).

    Or maybe WHS refreshes the dates of every used cluster, in the database every time it runs a backup. Changed clusters will be added and their old records will then be left with the old dates and only those get erased via pruning.

    If you are talking about files that would get modified periodically (i.e. an Excel spreadsheet), yes.  The new one would "replace" the old one in future backups and once the final backup containing the old one is not within the retention policy, the old one is deleted.

    These are the gory details I seek. ;-)
    To be honest, you're overthinking it.  :)  Ken already told you everything you need to know:  if a cluster is needed by any backup, it stays.  Otherwise, it goes.  Couldn't be simpler.
    Sunday, September 6, 2009 11:56 PM
    Moderator
  • Please read the words I wrote, and don't read into them based on your knowledge of standard backup strategies. I've already told you everything an end user of the product needs to know, and more.

    As long as a cluster stored in the database is "used" by even a single backup in the database ... it will be retained.

    A "backup" in the Windows Home Server backup database is little more than a long list of pointers to clusters of actual data, which are in the database as well. When all references to a cluster are removed from the database during the weekly pruning, that cluster will also be removed, not before.

    No gory details are available; they would have to come from Microsoft. Microsoft has published the Home Computer Backup and Restore technical brief (linked previously), that is the extent of the public information. Anything further would have to come from your own reverse engineering of the database (which, by the way, is a violation of the EULA).
    I'm not on the WHS team, I just post a lot. :)
    • Marked as answer by CSWG Wednesday, September 16, 2009 2:33 AM
    • Unmarked as answer by CSWG Wednesday, September 16, 2009 2:33 AM
    Monday, September 7, 2009 3:35 AM
    Moderator
  • Sorry for the delay, was out of town. What you said makes sense. Be rest assured I will never ride in one of those cars that automatically steer, when they come out. ;-)

    Thanks for the time and effort!
    Wednesday, September 16, 2009 2:39 AM