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What are the different phases of Cloud Backup / SnapMirror Cloud?

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Applies to

  • ONTAP 9
  • BlueXP Cloud Backup
  • SnapMirror Cloud (SM-C)

Answer

There are two main phases for Cloud Backup / SnapMirror Cloud (SM-C) backup

Data Transfer Phase
  1. VMAP Invalidation
    • VMAP is a metadata file which contains a mapping of ONTAP Block Numbers (VVBNs) to Cloud Block Numbers (PVBNs) which allows for maintaining deduplication savings and other features
    • In this step, ONTAP removes VVBNs that are not present in the backup Snapshot from the VMAP file
    • This step is valid for incremental updates only, not baseline transfers
  2. Generate a list of changed inodes / blocks
    • For baseline transfers, this identifies all inodes / blocks in a volume
    • For incremental transfers, this identifies all changed inodes / blocks between the baseline (most recent successfuly transferred) Snapshot and the current backup Snapshot
  3. For each changed 4K block (VVBN) in the changed files, make an entry in the VMAP for the VVBN and a corresponding "Pending" Cloud PVBN
  4. Pack data to-be-transferred into 4MB objects and write objects to the object-store destination
    • Object compression is applied prior to writing objects to the object-store destination
  5. Replace "Pending" Cloud PVBNs with actual Cloud PVBNs in the VMAP file
  • These steps are followed for L0 data (user data) followed by L1 and L2 data (metadata)
  • After L0, L1, and L2 data, a flat file is made with L3 pointers
  • ONTAP may report being busy with the following messages during this phase: WAFL_S2C_FIND_ENTS_TO_PROCESS_VMAP, WAFL_S2C_UPDATE_CPVBN_VMAP, and WAFL_S2C_READ_AND_POPULATE_INDIRECTS

NOTE: During steps that do not involve writing user data to the object-store, the Cloud Backup / SnapMirror Cloud relationship may report little to no changes in total progress

Object ID Bitmap Phase
  1. ONTAP generates the object_id bitmap from the VMAP
    • The object_id bitmap gives information about all of the objects associated with the Snapshot being backed up
  2. The object_id bitmap is written to the object-store destination along with the Snapshot
  • Generating the object_id bitmap during backup allows for efficient garbage collection and is a basis for other features
  • Garbage collection runs once a day and cleans up deleted Snapshots and their associated objects in the object-store destination
  • ONTAP May report being busy with the following message during this phase: WAFL_S2C_WALK_VMAP_OBJID
  • Larger volumes with more files will take longer to generate the object_id bitmap

Additional Information

  • There is a Request for Enhancement to provide detail around these phases and progress in snapmirror show output

  • Please contact NetApp Technical Support or log into the NetApp Support Site to create a case to get your request added as a vote to the enhancement request. Reference this article for further assistance.

 

 

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