Data Domain: PowerProtect DD Virtual Edition Metadata Guidelines

PowerProtect DD Virtual edition provides unmatched performance and total cost of ownership (TCO) for customers seeking the benefits of a Data Domain appliance in a virtual form factor. However, care must be taken before deploying DDVE in certain types of environments as they can lead to metadata usage over the prescribed guideline, thereby affecting the TCO. The increase in metadata resulting from the scenarios discussed below is a natural consequence of high deduplication as the product is working as designed. Dell Technologies highly recommends assessing the potential impact of the below scenarios on the TCO prior to deployment.

 

Using a backup application such as Avamar with Virtual Synthetic (VS) backups enabled can lead to a high deduplication ratio on the DDVE, at the cost of increased metadata usage. A high effective deduplication rate exerts a downward pressure on TCO, while increased metadata usage exerts an upward pressure. The resolution of these forces determines the overall TCO. Assess prior to deployment if the backup environment has this type of workload. In some environments, it is not possible to disable VS backups in the backup application or choose one that does not use VS. If this is the case, the only solution is to add additional metadata disks to keep the system operational.

 

Writing partial containers to the object store increases the metadata overhead of the system. These partial containers may be due to frequent commits or by writing small files (<1 MB). In this scenario, this spike is temporary, and space can be regained by running cleaning, which copies the partial containers forward and eliminates the fragmentation. However, there is a cost associated with running cleaning, which might affect TCO if run too often. The best practice guideline is to run cleaning once a week and size the metadata disks accordingly.

 

In cases where the environment has millions of small files (<1 MB), the metadata overhead is high compared to the data. This is an unsupported workload and DDVE might not be the right solution to protect such workloads.

 

Certain backup applications such as Oracle or Commvault introduce markers in the backup stream. DDVE deduplicates these markers, providing high deduplication rates. This leads to a tradeoff between a high deduplication rate at the expense of increased metadata usage. The user can choose to disable in-app optimization in the backup application and reduce DDVE metadata usage or choose the higher deduplication rates at the expense of increased metadata usage.

 

If it is not possible to disable in-app optimization in the backup application, the only solution is to add additional metadata disks to keep the system operational.

 

This scenario is uncommon, but like the others can lead to high deduplication rates, which might cause a significant increase in metadata usage. The only solution is to add additional metadata disks to keep the system operational.

 

In the specific scenarios described above, a significant increase in the metadata consumption is expected, and the recommended solution is to add additional metadata disks to keep the system operational. The product is operating as designed, and Dell Technologies highly recommends assessing the potential impact of the above scenarios on the TCO prior to deployment.

 

For workloads with a higher deduplication ratio, more metadata is needed. Metadata storage can be dynamically expanded. When the metadata storage space usage exceeds 80%, an alert is raised. A new metadata disk should be added to the DDVE immediately to avoid being out of space. Follow the administration guide for the procedure of storage expansion. Always use 1 TB disks.

 

The following command (documented in the DDVE Installation and Administration Guide) shows active local metadata usage. For example:

sysadmin@atos-ddve# filesys show space tier active local-metadata
Active Tier: local-metadata usage
Size GiB   Used GiB   Avail GiB    Use%
--------   --------   ---------   -----
 24290.4     4390.2     19900.2   18.0%
--------   --------   ---------   -----