a (hopefully) simple newbie zfs query regarding available space

[chris scott]

2009/8/9 John . <comp.john at googlemail.com>

> Hello list
>
> I followed instructions for ZFS on
> http://wiki.freebsd.org/ZFSQuickStartGuide, substituting ad6 and ad10
> (two new SATA3 1TB disks) for da0 da1 and da2 in the instructions. I
> was surprised to see only 993GB in /tank/. Is this expected, or is it
> user error? Also, these disks are completely unformatted. I expected
> to do a newfs or something similar, and for it to take a bit of time!
>
> This is on a running 7.2-STABLE amd64 system. It is only these two
> disks that I want as ZFS, the rest are UFS2
>
> cheers
> --
> John
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not a zfs thing is happens with all os and file systems. Basically HD
manufacturers quote their capacities in base 10 ie 1 TB = 1000000000 bytes.
File systems are calculated in binary therefore the calculation they use is
1024 x 1024 x 1024 = 1099511627776. Slightly more as you can see.

Therefore 1 GB is os terms is 1073741824

therefore hd capacity in GB is

1000000000000/1073741824 = 931.322575

The extra you see is it due to HD manufactures slightly over capacity the
drives