Add note to correct Nebbiolo1 disk space

[jwokaty]

Close #372

[jwokaty]

@hpages Do you have a preference for the location of information like this?

[hpages]

Maybe specify the path to the partition in your df command in order to reduce the size of the output:

biocbuild@nebbiolo1:~$ df -Th /home
Filesystem     Type  Size  Used Avail Use% Mounted on
data/home      zfs   1.7T  877G  852G  51% /home

Also it can be useful to use the -T option here to show the type of filesystem used for this partition.

I would suggest that you also show the df command the two times that it's used, even if it's the same command each time.

My understanding is that the issue of disk space being invisibly eaten by unwanted snapshots is zfs-speficic so could happen on any build machine where zfs is used. Also it could maybe happen in other contexts, not necessarily after an update. All this to say that maybe this section would be more useful in the long run if you slightly rephrase things to make it zfs-specific rather than nebbiolo1-specific.

More precisely, I'm thinking of:

• a more generic title for the section e.g. something like "Disk space invisibly used on zfs partitions" instead of "Nebbiolo1 missing disk space"
• a quick mention of the zfs snapshot feature and how it could sneakily reduce the visible size of a partition (i.e. the size displayed by df)
• a mention that this has happened on nebbiolo1, possibly after a system update (or was it after the OS upgrade from 20.04 to 22.04?)
• show how to diagnose (df -Th /home and zfs list -t snap commands)
• show how to fix (zfs destroy, zfs list -t snap, and df -Th /home commands)

I'm not sure about the best place for this. Moving it to a separate document means we're not necessarily going to remember to check the new document next time we have a "No space left on device" error. So keeping it here is fine for now, I guess. Maybe at some point we should start a section about how to troubleshoot "No space left on device" problems in general, and move the zfs snapshot thing to it (which is only one of the many ways we can end up with disk space problems).

Thanks!

[jwokaty]

Thanks for your comments.