Arup Nanda explains in his article skillset that are required for exadata administration, interestingly he puts storage administration skills 0%, that explains how oracle has revolutionized the storage layer, and bought in a concept of cell administration.
Oracle RAC DBA -- 60%
Cell administration --20%
System Administrator --15%
Network Administrator --5%
Storage administrator --0%
Oracle RAC DBA -- More importantly expereience in 11gr2 database with ASM(grid infra)
a full rack will come with 8 database server.Cluster can be configured depending on your requirement. you can have 1 cluster with 8 nodes,(for example- 5 production and 3 qa) or you can have multiple clusters.
Cell Administration -- done through "celladmin" user, using utilities such as "cellcli" or "dcli"
a full rack will come with 14 storage servers. there are 12 physical disk in each storage server or cell server.
The concepts here to learn are Cell, physical disks, cell disks, grid disks, and obviously ASM.
Network Administration --Infiniband swtich, full rack has 3 infiniband switch. You can imagine the network layer in between the database servers and storage servers. basic commands for monitoring like ping, rdpping. Can also be monitored through grid control, though at a very basic level i would imagine.