NetApp & Storage 相關名詞解釋
MTTDL: Mean time to data loss
MTBF: Mean time between failure
http://blogs.sun.com/relling/entry/raid_recommendations_space_vs_mttdl
RAID-DP: NetApp storage with double parity disk.
WAFL: NetApp proprietaries file system, Write Anywhere File Layout.
Redirect-on-writing: After a snapshot has been created, whe writing actions will be redirected to other free spaces.