We want to expand the SSD Tier in a VNX2 Pool, but unfortunately the array came with Fast Cache SSD's (SLC) in the Extreme Performance Tier of the Pool.
1) We now want to expand with cheaper Fast-VP SSD's (eMLC). Is this a problem?
2) Next question: I know it is against best practices, but can we expand the SSD Tier with bigger-size SSD's or do we absolutely have to stick with same-sized (200GB) SSD's? What is exactly the penalty if we go with bigger SSD's?
Re: VNX Pool SSD tier with mixed SLC and eMLC SSD's?
I'm going to say: no, and yes.
No, I do not believe that you are prohibited to expand with a different SSD type. What you probably can't do is perform a expansion mixing both types in a single RAID group.
Yes, you can use larger SSDs. The usual caveat is based on not wanting the bigger disks to end up with a disproportionate load, but that is far less of a concern with SSDs than it would be, for instance, with mixing 300GB and 1.2TB spinning disks.