Skip to main content

Troubleshooting Storage Issues, Refresh Older VDB(s) (KBA1025)






When VDBs are first provisioned, they occupy very little storage space on the Delphix engine.  Any blocks that are updated as a result of redo recovery during provision will occupy space but otherwise they share the underlying blocks of the source snapshot.

VDB space usage grows in two ways.

  1. Data modifications (inserts/updates/deletes) in the VDB consume extra storage. Modified data blocks cause the copy-on-write filesystem of the Delphix engine to allocate additional blocks to store changes that deviate from the original shared block.
  2. If VDBs are not refreshed for a long period of time (longer than the snapshot retention window of the source, typically 7-30 days), then Delphix must retain the blocks of the underlying source snapshot even though it might otherwise be eligible for deletion.  Holding the original source blocks for the dependent VDB translates into an increased storage requirement.

The amount of storage consumed by a VDB is often proportional to the length of time since it was provisioned or refreshed, as updates to the data result in new storage blocks being allocated which may then reduce the number of blocks shared with its source snapshot.  The time of the last provision or refresh can be seen from the current timeflow name in the Delphix engine CLI, as in the example below for VDB 'vdb10'.  The timestamp included in the VDB timeflow names represents the time in UTC when it was created by the most recent provision or refresh job.

delphix-engine> database
delphix-engine database> list display=name,currentTimeflow
DBOMSR8A1718  DBOMSR8A1718/default
vdb10         'DB_REFRESH@2022-01-12T10:18:24'
prac2         'DB_PROVISION@2021-12-17T11:44:22'

It may also be possible to find the time of the most recent provision or refresh job by entering the VDB name into the filter field on the Jobs page in the Delphix admin UI and setting an appropriate time period in the left-hand panel.  In the example below, the most recent DB_REFRESH job was started at 10:18:20 UTC on 12th January 2022, matching the timestamp in the current timeflow name to within a few seconds.


Storage space can be released by refreshing older VDBs, if your business requirements allow.



A VDB refresh will delete all existing data from the VDB and repopulate it with the chosen data from the source.

The recommended approach is to regularly refresh VDBs in a planned fashion, to reduce storage pressure. Delphix Services can assist you in predicting the space requirements for various refresh policies.