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Thread: Basic question about configuration

  1. #1

    Question Basic question about configuration

    Hi! I'm a new Zmanda Cloud Backup customer from Italy.

    I'm configuring a simply file system backup set for my Windows 2008 server.
    My target is configure something like this:
    - Full backup: never scheduled, only first time
    - Incremental backup: every night, with 1 week retain

    My logical doubt: is it this a valid configuration? Can Zmanda, after some months, rebuild a backups about few days ago with only one full (old) backup and last week incremental backups?
    From another point of view: Zmanda automatically "merge" the old full backup with the incremental backups before deletes them?

    The goal is to keep the full backup about one week ago and the incremental backups about the last week, building the full from the incremental ones (without re-uploading every week the full backup or keeping all the incremental from the last full backup)

    I hope i explain this clear!
    Thank you,

    Daniele

  2. #2
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    Hello Daniele,

    Unfortunately, that's not a good backup strategy with ZCB for two reasons.

    1. ZCB is built around the idea of a regular full backup. An "incrementals forever" approach just doesn't work very well. Every incremental in the chain makes ZCB work just a tiny fraction harder to keep track of which files are where, and makes restores take just a bit longer. Eventually the metadata required to keep track of the incrementals becomes unwieldy. You can go quite some time without a full backup, but eventually you'll need one. ZCB will actually force a full backup after 300 incrementals.

    This article talks a bit about the resources used by incremental backups and how to increase the maximum to 500, rather than 300. However, a periodic full backup is still necessary: [url]http://help.zmanda.com/x/3gI6[/url]

    2. Incremental backups are like links in a chain: you need them all. If you remove any of the links, you compromise your ability to do a full restore. This is different from a differential backup, which is sort of a "roll-up" of any changes since the full backup. You need every incremental, but you only need one diff.

    You may have noticed the checkbox labeled "Keep backup if a dependent backup exists" in ZCB, under the retention settings when time-based retention is chosen. This override keeps backups that depend upon each other (like incrementals that all need each other) from being purged even if they expire. You can disable that, but I strongly recommend against it.

    This article talks about differential vs incremental backups and even has a suggest schedule to reduce full backup frequency: [url]http://help.zmanda.com/x/1QI6[/url]


    In the end, the defaults presented by ZCB represent the best practice for most customers. The further you stray from those, the more you risk running into unintentional consequences like high resource usgae.

    There are multiple suggested options for scheduling, under the Schedule Template button. One of those templates for File System is a monthly full, weekly diff, and daily incremental.

    You could probably change the full backup in that template to be once every 3 months or so without risking performance issues unless you have a huge number of files (several million or higher) or your total data size is quite large (several hundred GB or higher).

    Let me know if you have more questions!

  3. #3

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    Hello Eric, thank you very much for your explanation, everything is very clean!

    After many articles and guides, I had understood what you're saying now:
    - with the "Keep backup if a dependent backup exists" flag checked, every incremental backups will be kept for dependence from the previous, although I define to retain only 1 week
    - without that flag, the system would be like "corrupted", because I would have some "orphan" incremental backups unusable

    The solution that i'm going to approach is this:
    - Full backup: never (only today)
    - Differential backup: weekly (on Monday night)
    - Incremental backup: every night

    Let me know if I understood correctly: in this way, choosing for "Incremental backup" the "1 week" retain (independently from retain of other backups that i'm keeping to default "1 day"), ZCB will deletes the old incremental and differential backups only when it will have 1 differential and 7(or 6?) incremental depentent children.. right?

    Last question: what about contemporary backups scheduled? Can i say to ZCB to skip the incremental backup in Monday night when will be run the Differential one?

    Thank you so much!
    Daniele

  4. #4
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    You will still need to do a full backup every now and then. Diff backups get larger over time. Eventually (depending on your data) it can get very, very large indeed. Taking a new full backup will reset the diff backups to their smallest possible size.

    You will need to disable the "Keep backup if a dependent backup exists" option if you want your retention to clear out the old diff + inc backups. If enabled, NO backup will be deleted until EVERY backup is ready to be deleted.

    However, if you disable that option, you may compromise your ability to restore.

    As for scheduling, you can tell ZCB to do a diff on Monday, and an inc on every day except Monday. Edit the schedule, change the "Every Day" dropdown to "Every Week", then select all the days except Monday.

    It won't skip automatically if both are scheduled.

  5. #5

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    Quote Originally Posted by Eric_R View Post
    If enabled, NO backup will be deleted until EVERY backup is ready to be deleted.
    Wait a moment: no backups will be deleted after enough differential backups??
    Simple example, after a first full backup:
    D1 <- I11 <- I12 <- I13 .... <- I16
    D2 <- I21 <- I22 <- I23 .... <- I26

    ... at this time, ZCB will not automatically delete all the D1 branch?? The D2 ones is enough for restore last 7 days... no?

    Quote Originally Posted by Eric_R View Post
    As for scheduling, you can tell ZCB to do a diff on Monday, and an inc on every day except Monday. Edit the schedule, change the "Every Day" dropdown to "Every Week", then select all the days except Monday.
    Thanks for the trick, it works!

  6. #6
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    Quote Originally Posted by officinaweb View Post
    Wait a moment: no backups will be deleted after enough differential backups??
    Simple example, after a first full backup:
    D1 <- I11 <- I12 <- I13 .... <- I16
    D2 <- I21 <- I22 <- I23 .... <- I26

    ... at this time, ZCB will not automatically delete all the D1 branch?? The D2 ones is enough for restore last 7 days... no?


    Thanks for the trick, it works!
    ZCB is strongly built around the idea of a regular full backup. It's not designed to go with a differential or incremental forever approach.

    As such, the retention enforcement isn't really smart enough to differentiate between your D1 chain and your D2 chain. It either protects them all, or none of them.

    D2 would be enough to restore within the last 7 days, but the retention enforcement knows that D1 exists and assumes you'd want to keep it so long as the other backups are around. You can disable the "keep backup if dependent backup exists" option to make ZCB delete after X days or weeks, but if you leave it on, D1 will be considered protected and will not be removed.

    However, once you turn off the "keep dependent" option, backups will be removed when the expire even if they're part of a chain, so you'll have some partial backup chains around.

    Sadly, you're trying to micromanage the program in a way that's a bit outside of its design. What you're talking about can--mostly--be done, but it won't be elegant or pretty.

    You could try this

    Differential every week, Retention of 2 weeks
    Incremental every day, Retention of 2 weeks
    Full backup, Retention of "forever"
    "Keep dependent backup" option OFF

    This would result in you having somewhere between one and two weeks' worth of fully restorable data at any given time, depending on exactly which backups have been purged.

    You'll still want to do another full backup eventually, since the diffs will continue to grow in size. And when you do, you'll have to manually delete the previous full backup.

    This will work, but it's not going to be as easy to manage as it would if you stuck to the defaults and the design of the program. You'll have to do some things manually, where if you stuck to the program's design, you could just sit back and let it work without intervention.

  7. #7

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    Thank you for support Eric, it's really very helpful.

    Some other little doubts:
    - The "Always retain .." and "Keep backup if.." flags work both on cloud and on local backups?
    - I've accidentally done the full backup today with retention "1 day". Can I change the retention without re-upload all?

    Thanks,
    Daniele

  8. #8
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    You're welcome.

    Both retention overrides (full backup and dependent backups) will apply to both local and cloud backups. You can't turn it off for local and on for cloud: it's either on for both or off for both.

    You can change retention for backups already done. Find your backup and/or upload on the Report page. Right-click it, then choose the Change Retention option.

  9. #9

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    Thank you Eric.

    The last two question (I promise that they're the last ):
    - There is a way (in ZCB client or in the web dashboard) to know who is the parent of an incremental/differential backup?
    - If I have into disk and cloud two different full backups and i haven't any incremental yet (it's the strange situation where i am now ), how the incremental backups works? The disk incremental will start from the full backup in the disk and the cloud incremental from the cloud one? Or both will start from the last full backup?

    Thank you very much for your support,
    Daniele

  10. #10
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    In the client, incrementals are numbered. Incremental 1, Incremental 2, and so on.

    Taking a new full backup or a differential backup will reset the count.

    That's about the only way to know.

    All child backups (diffs and incs) tie back to the most recent full backup taken; doesn't matter if it's on disk or cloud. The most recent one is the important one in that sense.

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