Home > Data Protection > PowerProtect DD Series Appliances > PowerProtect Appliance Data Invulnerability Architecture > No partial stripe writes
Traditional primary storage disk arrays, whether RAID 1, RAID 3, RAID 4, RAID 5, or RAID 6, can lose old data if, during a write, a power failure causes a disk to fail. This data loss occurs because disk reconstruction depends on all the blocks in a RAID stripe being consistent. During a block write, there is a transition window where the stripe is inconsistent, so reconstruction of the stripe fails, and the old data on the failed disk is lost.
Enterprise storage systems protect against this data loss with NVRAM or uninterruptible power supplies. However, if these protections fail because of an extended power outage, the old data could be lost, and a recovery attempt could fail. For this reason, Data Domain systems never update just one block in a stripe. Following the no-overwrite policy, all new writes go to new RAID stripes, and those new RAID stripes are written in their entirety. The verification after write ensures that the new stripe is consistent. New writes do not put existing data at risk. Data Domain systems are designed to minimize the number of standard storage system errors. If more challenging faults happen, less time is needed to find them, correct them, and notify the operator.