VDEVs Total Size vs Usable Capacity

TrueNAS General
1

I am new to TrueNAS SCALE and I have just completed my first installation. I created 3 different pools and I noticed that the Usable capacity of the pool is different from the Data VDEVs size (see screenshot as an example), this is true from all 3 Pools.

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chrome_liMaIhS2KF1586×460 45.1 KB

As per the screenshot why 32 GiB was lost from the actual disk size? Disk size = 931.51 GiB vs Usable Capacity = 899.25 GiB

What is the logical explanation for this disk space loss?

2

  1. In 23.10 and earlier by default you get a 2GB swap partition on each disk.

  2. There is a reserved space at the beginning of the drive for boot sectors, the GPT Primary Partition table, a legacy MBR and possibly GRUB. The ZFS partition is rounded to a specific sector boundary at the end too, plus there is a backup copy of the GPT partition table stored at the end of the drive.

  3. Then space is reserved for metadata e.g. the ZFS equivalent of directories and free-space lists and the journal (ZFS is a journaling file system).

This is just the way this stuff works - there are overheads.

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