On a space restricted filer, I can't help but notice that 9G of usable (post-tax) space is dedicated to vol0, which contains less than .5G of actual data. I tried an end-run around this:
Marie-NetApp> vol size vol0 -1g
vol size: Volume 'vol1' cannot be resized below 9 GB on this appliance because it is the root volume.
Marie-NetApp> vol copy start vol0 vol1
Marie-NetApp> vol size vol1 1g
vol size: Flexible volume 'vol1' size set to 1g.
Marie-NetApp> vol options vol1 root
vol options: Volume 'vol1' cannot become the root volume after a reboot because it must be at least 9 GB on this appliance.
Obviously this was a spectacular failure.
As a workaround, would there be any downside to expanding vol0 to take the entire aggregate, and then simply storing user data directories in it? In this particular case this is an FAS2020 with X268_SGLXY750SSX AQJZ 635.5GB 512B/sect drives. But the identical space reservation appears on other versions of Data OnTAP with other drive geometries. Is it just 9G no matter what?
From the System Administration Guide on root volume recommendations (7.2.7):
Size requirement for root FlexVol volumes
The root volume must have enough space to contain system files, log files, and core files. If a system problem occurs, these files are needed to provide technical support.
In contrast with traditional volumes, it is possible to create a FlexVol volume that is too small to be used as the root volume. Data ONTAP prevents you from setting the root option on a FlexVol volume that is smaller than the minimum root volume size for your storage system model, and prevents you from resizing the root volume below the minimum allowed size.
A root FlexVol volume must have a space guarantee of volume. Data ONTAP prevents you from setting the root option on a FlexVol volume that does not have a space guarantee ofvolume, and prevents you from changing the space guarantee for the root volume.
The minimum size for a root FlexVol volume depends on your storage system model. The following table lists the minimum allowed size for root volumes.
Storage system model
Minimum root FlexVol volume size
It is recommended that you avoid storing user data in the root volume, regardless of the type of volume used for the root volume.