New submission from Sander <sander.jonkers+git...@gmail.com>:
MacOS BigSur (and older), python 3.9.2 (and older)
For disks >4TB, os.statvfs() shows a wrong value for available space: too low,
and always rollover at each 4TB.
As 4TB = 2^42, hypothesis: rollover in 32bit counter (with 10bit blocksize)
Example:
"df -m" does show the correct available space
df -m /Volumes/Frank/
Filesystem 1M-blocks Used Available
Capacity iused ifree %iused Mounted on
//frank@SynologyBlabla._smb._tcp.local/Frank 21963360 2527744 19435615 12%
2588410474 19902070164 12% /Volumes/Frank
So available space 19902070164 MB, so about 18.5 TB. Good.
Now python's os.statvfs():
>>> s = os.statvfs("/Volumes/Frank")
>>> s.f_bavail * s.f_frsize / 1024**2
2658399.39453125
So 2.5TB, and thus wrong
The difference is 16777216 MB which is exactly 4 times 4TB.
Problem seems to be in MacOS statvfs() itself; reproducable with a few lines of
C code.
We have implemented a workaround in our python program SABnzbd to directly use
MacOS' libc statfs() call (not statvfs() ). A solution / workaround in python
itself would be much nicer.
No problem with python on Linux with >4TB drives.
----------
components: macOS
messages: 389596
nosy: ned.deily, ronaldoussoren, sanderjo
priority: normal
severity: normal
status: open
title: MacOS os.statvfs() has rollover for >4TB disks at each 4TB (32bit
counter overflow?)
type: behavior
versions: Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43638>
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