Hello, we have a FAS2050 running on the latest ONTAP 7.3.7 that is currently using 12 SAS drives: 2 parity (raid-dp), 9 data and 1 hot spare. These drives are all in rg0 and this portion of our NetApp is all LUN storage for VMware. We also use ASIS deduplication on all LUNs.
I have recently acquired 8 new SAS drives to fully populate this device and be able to gain some additional storage space. I am loosely following advice on commands found in this community forum, including this post which has been very helpful.
However, before I implement these changes, I have some questions and decisions I need to make. It seems that NetApp highly recommends that raid groups be equal size, or not off by more than 1 spindle. The size of my current SAS raid group rg0 is 16. My understanding is that this size can be increased, but not decreased. I believe the reason for the size of 16 is because additional SAS shelves that I might add in the future would contain 14 drives, as I understand. This would allow one to configure equal size raid groups between the primary and additional shelf.
However, without having the additional shelf in place, it seems that a decision needs to be made today that could affect future growth of this device. The decision seems to be whether or not we think we would ever add an additional shelf. If we do think we might, then it seems perhaps the additional drives should be added to an additional raid group now. If we do not think we would ever add that additional shelf, then it seems the drives we have today could all be added to one large raid group.
Please see the scenarios I've put together below, and tell me if I'm missing something here.
rg0 --> 2 parity + 9 data + 1 hot spare
Scenario 1: assume future growth, create additional raid group
rg0 --> 2 parity + 9 data today (expandable to 14 data drives in future)
rg1 --> 2 parity + 6 data today (expandable to 12 data drives in future)
+ 1 hot spare = 20 total spindles = 15 data drives
PRO: expandable in future with equal raid groups
CON: less data storage due to more parity drives; non-equal raid groups today
Scenario 1b: how the future would look after adding the 14-drive SAS expansion shelf
rg0 --> 2 parity + 14 data (fully populated raid group)
rg1 --> 2 parity + 14 data (fully populated raid group)
+ 2 hot spares = 34 total spindles = 28 data drives
Scenario 2: assume no future growth, enlarge current raid group to fully populate device
rg0 --> 2 parity + 17 data today (no way to expand and keep equal raid groups in the future)
+ 1 hot spare = 20 total spindles = 17 data drives
PRO: more data storage today due to less parity drives; performance improved today by not having non-equal raid groups
CON: performance could be impacted in future, if expansion became necessary, due to non-equal raid groups
If this is all correct, then I need to make a choice about future expansion. Of course I'm basing all these decisions on the assumption that non-equal raid groups is a "big problem," though I don't fully understand how much of an impact we're talking about here.
Lastly, I'm trying to determine if reallocation is advisable in my scenario. I do understand what reallocation is and why it's important. However, I read recently that it may not be advisable when the volumes are LUN storage (as mine are). Is there any argument for or against reallocation?