File system concepts (df command)

Question

I'm finding it difficult to understand some stuffs about the df command. Suppose I type df and I have the following output

Filesystem    1k-blocks    Used           Avail    Capacity    Mounted on
/dev/da0s1    some number  some number    number   percentage  /win
/dev/da0s2    some number  some number    number   percentage  /win/home
/dev/da0s3a   some number  some number    number   percentage  /
devfs         some number  some number    number   percentage  /dev
/dev/da0s3g   some number  some number    number   percentage  /local
/dev/da0s3h   some number  some number    -number     102%     /reste
/dev/da0s3d   some number  some number    number   percentage  /tmp
/dev/da0s3f   some number  some number    number   percentage  /usr
/dev/da0s3e   some number  some number    number   percentage  /var
/dev/da1s1a   some number  some number    number   percentage  /public

Are the answers to the following questions correct?

How many physical drives do I have? Ans: 2. da0s1 and da1s1

How many physical partitions on each disk? Ans: 8 for da0s1 and 1 for da1s1

How many BSD partition on each physical partition Ans: Impossible to determine. We have to use the -T to determine its type

How is it possible for the file system /dev/da0s3h filled at 102%? And where is this overflowed data written?Ans: I have no idea for this one

Thanks.

Solution

for bsd type filesystem, 102% is possible. for example, here is a similar issue by juniper http://kb.juniper.net/InfoCenter/index?page=content&id=KB21937&actp=RSS

the OS usually has some reserved space (default is 5% in linux, not sure about bsd variants), so it would seem that the negative is eating into the reserve and the OS is allowing it. long-term it may not be a good idea.

Comments

[mkab]

So the each OS have some reserve space for file systems. Didn't know about that. What about my answers to the other questions are they correct?

[johnshen64]

Yes, that is true, the reserve is usually for emergency so not meant to be used for long by applications. Your answers 1 and 2 are correct, but I am not that familiar with bsd flavors, though used it in various bsd-based devices and mac, so cannot really say much about your question 3.

[mkab]

Ok no problem. Thanks a lot for your help. Really clarified some stuffs for me.