MammaGutt wrote:
I would recommend reading the concepts guide. This will tell you how space is allocated from raw space on PD to usable space in VV.
Quick summary. Whenever a TPVV/TDVV wants to grow it will take available space from the VV. When the VV is "full" (ie, User Used = User Reserved), it will allocate new space from the CPG. When the CPG is "full" it will allocate new space from RAW space (PDs). When the RAW space for that tier is full, you basically have a full array. So a growing VV in a growing CPG will most likely be 99% "full".
3PAR will "borrow" space from a lower level to prevent an outage due to a full array if a tier is completely full (ie, if you write to FC layer and there is no more available RAW space there, it will use NL space to keep the system running). A lower level is of course slower, but I guess most people rather want to have a slow write, rather than no write. Be advised that clean-up after something like this might be time consuming depending on the amount of space written to a lower level, the number of VVs/CPGs affected and how full your array is when you've cleaned up/installed more hardware.
Reclaiming available space from VV is a background task. That space will be made available to the CPG. Reclaiming available space from the CPG is done by using compact cpg. If you only have one CPG, there is no harm in having a low amount of RAW space available as long as you have a lot of space available in the CPG, however it might be confusing having to look multiple places to get the "combined" available free space and if you have multiple CPGs on the same tier, the "combined" availble free space might differ from VV to VV as some space is most likely tied up in a CPG.
Hi All
What happens if the VV is already on the lowest tier NL?
What is meant to be the process in this situation which tier does it borrow from?
or does everything come to a grinding halt?
""Cheers