Transferring XVLs as links during object replication

Replication and Disaster Recovery Administration Guide for Hitachi NAS Platform

Part Number

When using object replication, the default behaviour is to 'rehydrate' data that has been migrated using either external migration or the Data Migrator to Cloud (DM2C) feature.

Files that have been converted to External Volume Links (XVLs) are copied in full to the replication target. This requires system administrators to ensure that there is extra space on the replication target. This is because the source filesystem only requires enough space to store a link to the externally stored data, whereas the replication target filesystem requires space for all the data.

If required, it is possible to copy XVLs to the replication target as links using the Transfer XVLs as links during object replication option and therefore remove the additional space overhead on the target system. This functionality can be enabled using the replication-xvl-as-links CLI command or by selecting the option on the File System Details page on the NAS Manager.

Note: To use this functionality, the NAS server containing the replication target file system must be able to access the migration destination, or a synchronised replica of it, in the same way as the source file system.

Considerations when transferring XVLs as links

  • Virtual Volume level migration paths - you can configure external migration paths for a Virtual Volume on a replication source file system. It is not possible to configure external migration paths on a replication target filesystem, because it is not possible to apply a path to a Virtual Volume. To transfer XVLs as links on this type of replication source filesystem, configure a file system level migration path on the replication target with the same name as the Virtual Volume level path on the replication source.
  • This option can be enabled on a filesystem that has existing migration and replication policies, but it only applies to migrated files that are replicated after the option is enabled. When the option is enabled on an existing replication source filesystem that has a cloud or external migration policy, you can re-format the replication targets to reclaim the space on the replication target that was previously occupied by rehydrated files. However, this requires a time-consuming full replication.
  • Once the option is enabled on the source, it cannot be disabled. This is to prevent the possibility of a broken configuration.

Using migration targets with replicated XVLs

There are two main methods of configuring migration targets for use with replicated XVLs:

  • Single migration destination for replication source and target
  • Separate migration destinations for replication source and target