Expanding a PV MD3600F+MD1200 with a MD1220

Hi all!

We are in a process of expanding our MD3600f SAN and I have a few questions about this expansion i hope someone can clarify a bit for me.

Todays setup are one MD3600f + MD1200 running with redundant Brocade 300 switches and attached to 7-8 Vmware PE610 servers. These arrays are fully loaded with 600GB 15K SAS drives in RAID5 with 1-2 Hotspares. This adds up to 9,22TB usesable storage for our VM hosts. This is our enterprise storage, and we also have a MD3000i with 1 attached MD1200 also in RAID5 for a lower grade storage such as documents, and other low IO data.

We are now in the process of replacing these VM hosts and are moving over to Hyper-V with a mix between storage spaces direct and the existing SAN. Reducing the amount of VM/Hyper-V hosts to 2-3.
In order to expand i'm adding a extra MD1220 starting with 10 pcs 1,2GB SAS 10K drives, and 1 HS. Attached to the Md3600f controllers. The idea is to setup the new volume in RAID10. This should give me aprox 6TB of usable data. I'm also considering adding some SATA SSDs for a new and fast volume. Will SATA SSDs be faster then the SAS drives, and if so any idea how much? SAS SSD are way to expensive at the moment but our new Hyper-V hosts comes with the ability to expand with 24x 12gbps disks in each host.

Should i expect a performance decrease when adding a second MD12XX to the SAN?

My questions is also regards the mix between SSD's and SAS drives. Should i buy a upgraded licence for the array and use the internal cache allowing the whole array to use the cache, or should i add it as a virtual disk and allow the VM/HyperV hosts access it? I.e adding OS drives to the SSD volume and data volums to a slower storage?

If choosing the internal solution, should the SSD's be seated in the 3600 or the 1220 array? My suspicion is that i will get a better result if they are located closest to the controllers...? Is it also recommended to have about 10% cache? Is this 10% of all disks added, or 10% of the RAID10 volume?

Do i need SSD's for both the 3600, 1200 and the 1220? Same question goes for the license upgrade, do i need to upgrade the license for all arrays?

Can i change the RAID level on the 3600 from 5 to 10 without dataloss, or do i need to move all my VMs over to different volume and re-configure the VD on the 3600?

When adding the new 1220 array with a 1,2GB (2,5 inch) hotspare, will this one also cover the other arrays with the 600GB 15K SAS drives?

Do anyone know how bit a performance boost i will get after moving over to RAID10 on both arrays?

All tips are deeply appriciated!

Cheers
Reidar