You can setup Single/Dual Redundancy on Tier level which means    Single Redundancy (RAID10/5) four your Tiers 1+2  and Dual (RAID6) only for your TIER3. About compression..... the data reduction (compression or compression/dedup) is a post process so it never effects the writes and when it comes to reads its configurable because you can select if you wanna only compress the frozen blocks or all blocks. If you select frozen (which is the default) than only the outdated data within a snapshot and which is already changed is compressed/dedup. We use dedup/compression for all data. Regards,Joerg
We are running two SC7020 and we are also utilizing Live Volume on most of our Volumes. Each SC7020 is also used with active VM's operating off each SC7020. Live Volumes xcross over both SC7020.. I have read that all writes will first be written too tier 1 storage, does this apply to the live Volumes. ?  As for live volumes as they will only be used in the event of a failure with the Source SC7020, Can Live Volumes be moved to Tier 3 Storage ?.  Also SNAPSHOTS are also active on the Secondary Live Volumes.. Is this necessary. ?  Each nigh start at 7pm our SNAPSHOTS are process and the moving of data between the Tiers begin, this process takes more than 4.5-6 hours to complete and really loads up the SAN IOPS and Disk Activity.. I/O waits climbs to around 35-45.. All Active Servers are VM's. We also operate 24/7. Thoughts on how to improve..  Last question, we were not aware that SC7020 would use Dual Mirror, we were not aware this would eat up storage space by a 1gb uses 3gb storage, we have thinking to turn off Dual Mirror on our Tier 1 and Tier 2 storage, and or turn on compression.. Thoughts.         
Live Volume - Between two SC7020