Data Invulnerability Architecture (DIA) is an important EMC Data Domain technology that provides safe and reliable storage.

The EMC Data Domain operating system (DD OS) is built for data protection. Its elements comprise an architectural design whose goal is data invulnerability. Few technologies within the DIA fight data loss. They include End-to-End verification and fault avoidance and containment etc.

Since every component of a storage system can introduce errors, an end-to-end test is the simplest way to ensure data integrity. End-to-end verification means reading data after it is written and comparing it to what was sent to disk, proving that it is reachable through the file system to disk, and proving that data is not corrupted.

The process of end-to-end verification:

1.     Receives writes request from backup software

2.     Analyzes data for redundancy

3.     Stores new data segments

4.     Stores fingerprints

5.     Verifies, after backup I/O, that the DD OS can read the data from disk and through the DD file system

6.     Verifies that the checksum that is read back matches the checksum written to disk

If something goes wrong in this process, DD OS is corrected through self-healing and the system alerts to back up again.

Fault avoidance and containment:

Data Domain systems are equipped with a specialized log-structured file system that has few import benefits.

1.     New data never overwrites existing data

Traditional file systems often overwrite blocks when data changes, and then use the old block address. The Data Domain file system writes only to new blocks. This isolates any incorrect overwrite (a software bug problem) to only the newest backup data. Older versions remain safe.

2.     Fewer complex data structures

In a traditional file system, there are many data structures (for example, free block bit maps and reference counts) that support fast block updates. In a backup application, the workload is primarily sequential writes of new data. Because a Data Domain system is simpler, it requires fewer data structures to support it. As long as the Data Domain system can keep track of the head of the log, new writes never overwrite old data. This design simplicity greatly reduces the chances of software errors that could lead to data corruption.

3.     Non-volatile RAM (NVRAM) for fast, safe restarts

The system includes a non-volatile RAM (NVRAM) write buffer into which it puts all data not yet safely on disk. The file system leverages the security of this write buffer to implement a fast, safe restart capability. As it restarts, the Data Domain file system verifies the integrity of the data in the NVRAM buffer before applying it to the file system and thus ensures that no data is lost due to a power outage. For example, in a power outage, the old data could be lost and a recovery attempt could fail.

4.     No partial stripe writes
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 (there are no partial stripe writes). New writes don’t put existing backups at risk.

Data Domain systems are the only solution built with this relentless attention to data integrity, giving you ultimate confidence in your recoverability. The innovative Data Invulnerability Architecture lays out the industry’s best defense against data integrity issues.

                                                                                                                                              

Author: Leo Li