[zfs-discuss] RAIDZ-2 disk space

Klaus Hartnegg hartnegg at uni-freiburg.de
Sat Apr 7 19:13:56 EDT 2018


Am 06.04.2018 um 00:04 schrieb Andreas Dilger via zfs-discuss:
> 480GB = 480000000000 bytes / 1024 / 1024 / 1024 = 447 GiB
> 
> Disks are sold with decimal "GB" to make them look larger

If you want to compare sizes, it is safest to compare on the level of 
bytes, because programmers still do not agree what kilo, mega, giga, 
etc. should mean.

ZFS report bytes with the -p option, e.g. 'zfs list -p'.

Windows shows bytes in the properties windows of files and disk drivers.

The Linux ls command can use either base 2 or 10 (option --si).
See 'man ls'.

Ubuntu starting with version 10.10 uses IEC prefixes in the GUI to make 
clear where they use base 2 instead of base 10.
See https://wiki.ubuntu.com/UnitsPolicy

Apple has switched from base 2 to base 10 with MacOS 10.6
See https://support.apple.com/en-us/HT201402

Harddisk manufacturers have always correctly used base 10. There is a 
myth that they switched from base 2 to 10, but that is not true.

Windows is the only major operating system that keeps doing it wrong: 
they use SI prefixes, eventhough they use base 2, i.e. divide by 1024.

There is (was?) an article where Microsoft officially confirms that this 
is a bug, but they do not dare to fix it, because too much would break. 
Unfortunately I cannot find that webpage again. If anybody has the link, 
please send it to me.


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