Partition size slightly different in File Manager

Discussion in 'backup, imaging & disk mgmt' started by Snoop3, Jul 17, 2015.

  1. Snoop3

    Snoop3 Registered Member

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    Hi,
    this is probably a rudimentary question but if i make a partition with GParted or apparently most other partition managers and i try to make it for example exactly 10240 MB so it will be 10 GB, it usually shows as 9.99 GB in a file manager when i'm in Win 7 or Win XP. Is there a solution to this?
     
  2. taotoo

    taotoo Registered Member

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    Make the partition 10mb bigger?
     
  3. Robin A.

    Robin A. Registered Member

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    Perhaps you can´t have a 10240 MB partition because this doesn´t correspond to an exact number of clusters or sectors.
     
  4. amarildojr

    amarildojr Registered Member

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    That's because formatting the partition will "take away" around 5% of it's total volume, for a self-reserved area.
    You're welcome, you can now mark this thread as solved :D hehehehe
     
  5. Snoop3

    Snoop3 Registered Member

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    maybe, i don't know enough about that.

    maybe thats for an previously unformatted drive. if i add one or two MB to each partition then they read as say 10.00 GB or 5.00 GB even. but i thought there might be some kind of option to fix this while setting up, like "align to cylinders" or "align on 1 MB boundaries" - something, idk what. i thought other people would have noticed this and it bother them a little too.
     
    Last edited: Jul 18, 2015
  6. amarildojr

    amarildojr Registered Member

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    That is mostly due to a confusion on your operating system, in this case Windows. Obviously it wouldn't show something like "9.98718 GB" so it decides it will either show 9.99GB or 10, depending on which value comes closed to the actual partition size.

    In Linux, if you correctly create the partitions (GParted does that) it will show as the correct size. See: https://i.imgur.com/wKR5sfb.png

    In my case, I have a 931.5 GB drive ("1TB"). I create the following partitions:

    • 1 GB, for /boot
    • 8 GB, for /swap (not shown there, it's normal)
    • 60 GB, for /
    • and the rest for /home
    The math fits perfectly. So don't worry, even though Windows shows your partitions as smaller, they're actually the size they should be. But as the partitions themselves have a sef-reserved area, only the useful area is shown on Windows :)
     
  7. Snoop3

    Snoop3 Registered Member

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    yes, i think thats correct.
    it looks like GParted or whichever partition manager peels off 1 MB at the front of each partition created? and then i think it reads as say 10.0 GB when viewed with GParted.
     
  8. amarildojr

    amarildojr Registered Member

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    No, that's not correct. Please read my other comment again.
     
  9. Snoop3

    Snoop3 Registered Member

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    ok, im not sure what you're saying. im starting to think maybe they place partition table info or MFT or something in this 1 MB?

    does your linux file manager show that 60 GB partition as 60.0 GB?
     
  10. pandlouk

    pandlouk Registered Member

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    It is caused because of the PBR/VBR (partition boot record/volume boot record). The first 16 sectors (16*512= 8kb) are reserved and windows ignores them when it displays the partition size.
    http://ntfs.com/ntfs-partition-boot-sector.htm
    Just add 1 to 5 mb to the partition and windows will display 10GB instead of 9.99GB.

    Panagiotis
     
  11. amarildojr

    amarildojr Registered Member

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    What I'm trying to tell is that it's normal behavior for Windows to show different partition size values once you format a partition. A partition, depending on which filesystem it uses (e.g. NTFS, ext4, etc), will have a self-reserved area, within that same partition. This alone will cause Windows to read the 10 GB partition size as "9.99 GB" = not because the partition is 9.99 GB in size, but most likely because that is what Windows "sees" as usable (because the rest (0.1 GB), which is reserved for the partition itself, can't be touched for the "health" of the partition), and that is completely correct in Windows.

    There's no fixing it, because this is normal in Windows.
     
  12. Snoop3

    Snoop3 Registered Member

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    thanks both for this good info. i think i start to comprehend it now.
     
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