Data Recovery from RAID5 disk - Promise Pegasus with Apple OSLion and Thunderbolt connection

It sounds like you may only need to rebuild your partition table if you didn't actually remove any data. I would boot a rescue cd and give TestDisk a try to see if it detects the 'lost' partition(s) during a 'Quick Analyze'.

Unfortunately, testdisk is less than awesome at repairing HFS+ partitions so you'll have to take the partition information it gives you and feed it to pdisk.

Overview of steps:

./testdisk /dev/sda1 
Analyze / Quick Analyze
Note starting block and number of blocks in partition
Boot Lion Recovery Mode
Drop to terminal
pdisk /dev/disk0
c
enter start block
enter number of blocks
enter name
w
q

Above referenced from Repair HFS+ Partition table