freshly formatted 4TB drive with gigabytes of space already used
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  1. #1
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    Question freshly formatted 4TB drive with gigabytes of space already used

    I have iscsi NAS with 2 x 2TB drives in one logical volume on the target server.

    VG #PV #LV #SN Attr VSize VFree
    iscsi 2 1 0 wz--n- 3.63t 0

    LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
    nas iscsi -wi-ao---- 3.63t

    When I do 'df -h' on the initiator server, It shows 3.8G being used.

    Filesystem Size Used Avail Use% Mounted on
    /dev/sdc 3.7T 3.8G 3.7T 1% /iscsi-nas

    This drive was freshly formatted with XFS.. why does it show this space being used when nothing is on it?

  2. #2
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    why does it show this space being used when nothing is on it?
    Ah, but there is. It just doesn't happen to have any of YOUR data on it yet, but it now has all the necessary journal/structure/control info to correctly handle your data when you start putting it there. That's what formatting a disk does. ;-)
    Change - the only constant.

  3. #3
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    Sure takes up a large chunk of space. Is that like metadata? What % does XFS need?

  4. #4
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    It'll be a % of the drive size. Others here will know lots more particulars about it than I.
    Change - the only constant.

  5. #5
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    I use a number of 2tb ext4 drives, df always shows 1.8tb free space when formatted but empty.
    ======
    Doug G
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  6. #6
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    there's also a conversion between Bytes and Tebibytes to take into account. the reported values in the first post are fine. XFS seems to reserve far less than ext4 does by the way for the purposes mentioned in post #2 above. I don't know the exact values either but typically around 1% for XFS is normal

  7. #7
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    Beyond the loss to formatting mentioned in post 2, ext4 reserves 5% of partition space by default for reserve. reserve is for disaster recovery when something has filled up all the other space on the disk, only root user can use the reserve. It only really makes sense to reserve on the OS partition. Unfortunately ext4 formatting doesn't distinguish what the partition is used for so it just reserves 5% for everything.
    You can recover the reserve space by setting the -r option to 0

    sudo tune2fs -r 0 <partition name>

    like "sudo tune2fs -r 0 /dev/sdb1"

    A while back ext3 / 4 reserved 10%, even 5% is a huge loss for multi TB drives (4TB @ 5% = 200GB)

  8. #8
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    Re: freshly formatted 4TB drive with gigabytes of space already used

    {Thanks for that, marko. It's nice to find out info like that}
    Change - the only constant.

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