I remember when we upgraded to Data ONTAP 8.0.2 it was recommended that we expand our current OS volume size from 80gb to 250gb. We have had ONTAP 8.0.3 running now for a little over a month and the volume is 72% full, I was just wondering if I needed to expand this volume again to accommodate for the new OS.
It depends on the controller model. For 6200 series it is 250GB for 8.0 then 300GB for 8.1. I have seen it work not increasing, but for support purposes I would follow the best practice and increase root to the minimum size in the ONTAP documentation (250GB for 8.0 likely for your FAS platform).
We are running FAS3170's. I have noticed that it does not continue to grow. It was just a substantial jump from the amount of disk usage that 8.0.1 used. If i remember correctly we were using about 6% of 80gb with 8.0.1 and now we are using 72% of 250gb with 8.0.3. I have gone though and made sure unneeded upgrade files and things of that nature are cleaned up.
3170 is the same 250GB size for 8.1 too so the same requirement when you upgrade again. It seems to work no issues when smaller like you are reporting though...but I think if you ever migrate root and run "vol options volname root" to mark the new volume root it might enforce the size but if you never move it likely won't be an issue but the docs call out minimum 250GB so it could be a support issue if you open a case for any reason.