Hi Michael,
The below is what we are using, it fits us and our needs:
Volume, Auto-Grow - On or Off ? > on
Volume, SnapShot Auto Delete - On or Off ? > on
Volume Gaurantee - On or Off ? > off
Volume SnapReserve - 0% ? > off
LUN space reserved - On or Off ? > off
What about Fractional Reserveration (does it make a diff, or is it ignored?) > must be set to 100 i you want to set vol guarantee to off, this is true for our ontap version, 7.2.5.1
PRO: what we have achieved with this config is everything is thin provisioned (vol guar. off and lun space reserve off), which allows for max disk utilisatin rates = good ROI.
Space monitoring only takes place at aggr. level (easier than monitor at volume level, snap reserve used etc) this allows for better reporting/trending.
snapshot autodelete: this has got PROs and CONs attached to it in my opinion. the pro is that once a volume cannot grow anymore (you do need to set a max size a vol is
allowed to grow to) deleting snapshots should provide free space for the writes in the volume. The CON is that if your snaps are backups and regarded as such they are exposed to
getting deleted.
CONs: ideally you d want to know your growth rate before engaging this, or you could phase it in by thin provisioning and then add 1 more snapshot at the time. The other
con is that you could end up in a situation where you have set a vol max autosize on that the aggr. cannot cater for, so your aggr will fill up. this is easy to manage though
once you have growth rates. The final con is that in theory even with snap autodelete on unless you allow your volume to grow enough you could up with running out of space
in a volume. In reality this has not happened to us once as we keep track of aggr. space usage and never allow them to go above 90%.
In short: the config. above is thin provisioning which by nature shifts workload into space management (operations manager is your friend) which in turn increases ROI on disk
space VASTLY. Just by turning on TP here we gained around 15TB back which at our costs are worth 300K AUD of cost avoidance.
This is what we are paid for I reckon ;-0
Hope this helps.
Eric