Quote:
we have 2x 2node/4cage 8200, each one has those SSD:
16 old 480 MLC + and 8 new 1,82 cMLC
You have two separate 8200s or a single 8200 shelf of disk (with 2 nodes) + 4 cages?
When you say each one of those has 16 old and 8 new, does that mean you have 5 sets of 24 SSDs? 1 tray for the node shelf, plus 4 additional dumb shelves?
I am trying to visualize the number of SAS loops and how your shelves are attached, and more importantly how many of the NEW SSD's there are per SAS loop. If you have enough new SSDs per SAS loop that write performance will be bottlenecked by the loop and not the PDs, then it might be ok to leave them all in one CPG.
After rebalancing, and all your PDs grow to the point that the 480gb drives are full, your new writes will be concentrated on the new drives. On a 4 node system, 32 drives was the sweet spot when the SAS loops limited performance, and adding more SSD was for capacity only. Making an educated guess that 16 drives is enough to push a 2 node system at full speed. So if your baseline is writing to 120 SSD drives (bottlenecked by the SAS controllers), and reach a capacity point where you are only writing to 48 drives (also bottlenecked by SAS controllers)... I think you are safe.