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High LA backups

Discussion in 'Data Protection' started by Sanyh, Apr 29, 2009.

  1. Sanyh

    Sanyh Member

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    hi
    i create full backups my server on 2:00 pm with tar.gz compression, but LA grow 10-15%. How make low LA on backups? and backup proceed to 10:00 AM (very long time)
    Backups make on second hard drive. Harddrive SATA 500 Gb.
     
  2. cPanelDavidG

    cPanelDavidG Technical Product Specialist

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    Can you elaborate what you mean by LA? Are you referring to latency?
     
  3. Vinayak

    Vinayak Well-Known Member

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    By LA, OP must be meaning Load Average.
     
  4. cPanelDavidG

    cPanelDavidG Technical Product Specialist

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    That makes sense.

    In the case the OP is referring to Load Average, keep in mind that these backup processes take place at nice +19 (lowest priority). Running at nice +19 allows other processes to grab the CPU first and allows the backups to proceed only when essentially nothing else is happening to ensure backups don't drag down the server's performance. This also makes this process take a very long time to complete compared to if it was running at nice 0.

    However, here's where we graze the technical details of what constitutes load average. Load average (in an very simplistic definition) is the average number of processes waiting to use the CPU over a period of time.

    When you have something running at nice +19, that means it is purposefully waiting for essentially everything else to use the CPU before it uses the CPU. So this process, while running at nice +19, is making the Load Average go up because it's often waiting. It's not that the server is busy or overloaded but the backups process is almost always waiting for the CPU before doing its job (as it should running at nice +19) and thus the load average is being thrown off (accurately so) by this nice +19 process.

    Here's an analogy to clear things up: Imagine you're tracking the average length of a line at a check-out counter. However, there's one person that really wants to take things slow (maybe they are being nice and letting everyone with 1 or 2 items go in front of them since they have a shopping cart full of stuff), so they let everyone else that wants to be on the line go in front of them. Only when there is no one wanting to be on the line will this person let the cashier tend to them. Since this individual was letting everyone else go in front of them, this skews the average length of the line as this person was always standing in line letting others cut in front of them.

    It's not a perfect analogy, but I hope it helps everyone better understand the mechanics of what's happening when an application is running at nice +19 and why the load average increases when that nice +19 process is running.

    This is not a comprehensive technical review of load averages. For example, load averages are weighted averages. You can read more at:

    http://en.wikipedia.org/wiki/Load_(computing)
     
    #4 cPanelDavidG, Apr 29, 2009
    Last edited: Apr 29, 2009
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