Looking for advice on re configuring disk groups in a pool

[sg611]

So I'm no SAN expert, but I'm working a job and would like some recommendations for the best way to create a pool for work.

Right now, we have 72x 2.4TB disks (3 spare), split between 2 pools. Each pool has 3 disk groups.

Pool A has 39 disks with 83.9TB available. Disk Groups:
A1: Raid 5 - 16 disks - 11.1TB / 35.9TB
A2: Raid 5 - 7 disks - 0 / 14.3T
A3: Raid 6 - 16 disks - 8.7TB / 33.5TB

Pool B has 30 disks with 62.3TB available. Disk Groups:
B1: Raid 5 - 16 disks - 13.7TB / 35.9TB
B2: Raid 5 - 7 disks - 0 / 14.3TB
B3: Raid 6 - 7 disks - 0 / 11.9TB

There are 3 spares, no SSDs, and no read-cache disks.

There are 4 volumes:
Vol1 (Pool A): 10TB - 2.7TB Allocated
Vol2 (Pool A): 55TB - 35.4TB Allocated
Vol3 (Pool A): 47TB - 25.6TB Allocated
Vol4 (Pool B): 62TB - 48.4TB Allocated

Should I keep an equal amount of disks in each disk group?
How many disk groups should I have?
Why did someone setup different RAID levels?
What can you recommend for this?

Thanks

[JonPaul]

@sg611 
Which generation/model of MSA do you have?
HPE Provides a 'Sizer' guide but that currently only supports the MSA Gen6 (1060/2060/2062) and the recently released MSA Gen7.
The sizer guide when used in Automatic mode will configure a system based on capacity and workload needs.
When used in manual mode it allows you to manipulate the configurations and shows what can be expected performance output.

HPE does not recommend using RAID5 for any spinning media.
There is a Best Practice Guide for your MSA Model which will have recommendations as well.  If I assume that you have Gen5 or Gen6 then you are using virtual storage and Pools. Which the recommendation is to have all disk-groups in a Pool be of the same configuration. (the data from your volume will be spread across all DGs in the Pool and performance will be inconsistent if the underlying DGs are not the same).  Lastly there is a performance degradation in certain workloads for disk-groups which do not conform to "Power Of 2" data disks (2, 4,   which is RAID 5 with 3, 5, 9 drives and RAID 6 with 4, 6, 10 drives.  
If you have an MSA Gen6 then use the MSA-DP+ RAID level,  it's a RAID 6 under the covers but allows up to 128 drives in a single disk-group and resolves many of the limitations that are included in virtual storage.
There is a 'Virtual Storage Technical Reference Guide' for your MSA Model as well which will have more details on how virtual storage works and MSA-DP+ RAID level

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