brilliant

That explains why I heard different things.

Just to confirm is this correct:

Flash T1 and T2 it would flush data down to free up T1 and then write to T1?

If we had T1 flash but T2 spinning it would write to T2 directly till DP could free up T1?

If T1 was 15k and T3 was 7k it would write driectly to T3 if T1 was full?

Flash T1 & T2 - ODDP would prevent T1 from filling and manually run ODDP to push data out of T1 once I believe it hits around 90% utilization

Flash T1 & Spinning T2 - works the same way as above

---- You generally dont want ODDP doing forced write flushes, you want to try to have enough capacity for the writes to flow more "normal" down the tiers. Lots of writes + forced flush at the same time = possible slowness in performance

All Spinning - yes it would if your profile allows it, sometimes we see systems that are using R10DM "unexpectedly" because the system was forced to do writes in T3. 

depends if it's flash or spinning and what profiles you use:

flash for tiers = On Demand Data Progression will force flush data out of T1 to T2 to keep space free

Spinning = If your storage profile (Recommended for example) allows it, it'll force write into the lower tier under DP can free up space in T1.

Ah ok, 

That makes sense. So instead of a force flush, a good idea would be to have a replay profile that ran every 5 hours or so, automatically freeing up the space and moving it to Tier 2.

This would prevent the Tier 1 from filling up.

Ok that is exactly what I have been thinking, thank you for confirming!