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Delphix

Troubleshooting Storage - Changing Snapshot and/or LogSync Retention

Snapshot policy for both dSources and VDBs are configured individually under the Manage > Policies screen. The "Default SnapSync" and "Default VDB Snapshot" default policies are configured to create snapshots once/day at 3:30am local time and the "Default Retention" policy is configured to retain data for 7 days. The amount of storage occupied by an individual snapshot is directly correlated to the amount of unique block changes between the consecutive snapshots.

Storage occupied by individual Snapshots can be determined under the Manage > Capacity screen after expanding the entry for a specific dSource/VDB as shown below...

If individual Snapshots are occupying excessive storage, check if the retention policy associated with the dSource or VDB can be reduced, provided such a change meets Business Service Level Agreements (SLAs).

If the snapshot retention policy for the dSource or VDB cannot be changed, and even the retention policy for the individual snapshot cannot be changed, determine if the retention policy for database logs can be reduced in the policy for the dSource or VDB. If it is not necessary to provision or refresh VDBs at a precise point-in-time throughout the entire time that snapshots are being retained, then storage can be freed up by only retaining database logs for a shorter time.  Doing so would mean that VDBs cannot be provisioned or refreshed to any arbitrary point-in-time beyond that retention point, but they can still provisioned or refreshed to the point-in-time of a snapshot.  This can alleviate storage pressure.

Many Delphix customers craft their policies to retain snapshots for a much longer duration than logs.  Snapshots are typically far more efficient, because a block which is changed 1000 times daily is stored 1000 times in transaction logs, but only one time in a daily snapshot.  For some customers, LogSync is not required at all, and disabling it can yield significant storage savings.

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