FAST Cache Rebuild

Hi,

We have 2 VNX5800's and the FASTCache is undersized from what EMC have told me after doing some Advanced Analysis. Its currently got 4 disks in and we want to double it to 8 in total. I understand the process of deleting the existing cache and then creating it again but what no one at EMC can or will tell me is how long this takes.

Before i go raising changes with our client they are going to want to know especially during the creation as Write Cache is disabled on the SP's from what i've read.

VNX5800

Existing FASTCache to remove - 4x 200Gb SSD's - Total Usable Approx 366Gb

Planned New FASTCache size - 8x 200Gb SSD's - Total Usable Approx 732Gb

I understand it will vary between arrays and depend on what is going on at that particular time but i wondered if anyone out there has an experience of deleting and re-creating the cache and can give me some idea of how long it took to complete. It would be appreciated.