STH Forum ZFS Snapshots - guess how much data

Discussion in 'Software Stuff' started by Patrick, Dec 10, 2015.

  1. Patrick

    Patrick Administrator
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    I just wanted to take a quick poll.

    STH forums run in their own Ubuntu VM using ZoL with Proxmox/ Debian as the base hypervisor distro. The volume has a total size of 40GB.

    Here is my crazy question for you: day to day snapshots how much data changes?

    Code:
    zfs send -nv -i sasarray1/vm-102-disk-1@sthforum20151209 sasarray1/vm-102-disk-1@sthforum20151210
    What is the total estimated size ______?
    
    I have to say, I was a bit surprised at first. It does at least give some idea how much data is changing on the disks daily.
     
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  2. pgh5278

    pgh5278 Active Member

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    A total wag with no basis - 15GB
     
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  3. mstone

    mstone Active Member

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    couple hundred megs?
     
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  4. Jeggs101

    Jeggs101 Well-Known Member

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    A few logs and a few text database updates. How big could that be? 10MB? 50?
     
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  5. Naeblis

    Naeblis Active Member

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    less than 2mb
     
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  6. TuxDude

    TuxDude Well-Known Member

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    I'll guess in the 2-3 GB range.
     
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  7. canta

    canta Well-Known Member

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    1G on my bet haha!
     
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  8. Patrick

    Patrick Administrator
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    Ending the suspense - it turns out the forums generate 600MB or so per day of snapshot delta or about 1.5% of the total volume size (but there is a lot of free space.)
     
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    eva2000 likes this.
  9. Mike Bailey

    Mike Bailey Member

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    @Patrick: What stack are you running for the actual forum software? If I had to guess, it's unlikely the VM itself generates much in the way of anything beyond incremental DB changes and some logs.

    Just guessing, logs might be no more than 100 MB a day, if that. Database changes? Easily not a lot. If you look at the actual underlying data files, most DB engines do a very good job of making sure they can make changes in place without having to split the pages in an index.

    That being said, 100 - 200 MB of writes to a database, especially if it's new content added on, will only amount to a small amplification factor in terms of disk churn.
     
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