Dell PowerStore Importing External Storage to PowerStore Guide

Restrictions and limitations for NFS-only VDM file import

The following restrictions and limitations relate to an NFS-only VDM file migration from a VNX2 storage system to a PowerStore cluster:

• Only Unified VNX2 storage systems are supported as the source storage system in a VDM file import.
• Only VNX2 storage systems with operating environment (OE) version 8.1.x or later are supported.
• Upgrading a PowerStore appliance when an import session is in progress is not supported.
• Creating an import session when an upgrade session is in progress is not supported.
• PowerStore supports a VDM import session with at most 500 file systems on the source VDM.
• The destination system must have enough available capacity to host the source resources to be imported.
  • PowerStore appliances use a different file system layout than Unified VNX2 storage systems. PowerStore appliances use UFS64 file systems while VNX2 storage systems use UFS32 file systems.
  • Import of deduplication settings is not supported.
  • A versioning file and fast clone are imported as a normal file. PowerStore appliances with operating system versions earlier than 3.0 do not support file-based import and File Level Retention (FLR) PowerStore appliances with operating system version 3.0 and later support file-based import and both FLR-E and FLR-C.
• Only uxfs-type file systems are imported from the VNX2 source VDM. Import of non-uxfs-type file systems or file systems that are mounted on a Nested Mount File System (NMFS) file system are not supported.
• A file system whose mount path contains more than two slashes is not supported. The destination system does not allow file systems with a name containing multiple slashes, for example, /root_vdm_1/a/c.
• Import of a file system that is a replication destination is not supported.
• Import of a checkpoint or checkpoint schedule is not supported.
• If the source replication file system is also the destination file system of a VDM import session, failing over the replication session (synchronous or asynchronous) is not allowed until the import is complete.
• Restrictions that are related to Quota import:
  • Import of group quota or inode quota settings is not supported. (The destination system does not support either.)
  • Import of a tree quota whose path contains single quotation marks is not supported. (A VNX2 system can create it but it cannot be queried or modified.)
• A VAAI operation is not allowed on either the source or destination systems during and after cutover.
  • A VAAI operation is not allowed on the destination system before cutover.
  • A VAAI operation on the source system must finish before cutover.
• Limitations that are related to Host access:
  • After cutover, read access performance degrades until the related file is imported.
  • After cutover, write access performance degrades until the VDM file migration is completed.
  • After cutover, a host cannot write data when the source file system is in the read-only mounted state.
  • PowerStore appliances running operating system version 2.1.x or earlier do not support FLR, and the default import setting is to not import such file systems. However, you can override the default, and those file systems are imported as normal destination file systems (UFS64) without FLR protection. This means that after cutover, locked files can be modified, moved, or deleted on the destination PowerStore appliance, but not on the source VNX2 system. This discrepancy can cause the two file systems to be in an inconsistent state.
  • After cutover, a host cannot access data when the destination file mobility network cannot access the source file system, which includes the following cases:
    • The network between the source VDM file migration interface and the destination file mobility network is disconnected.
    • The source VDM is not in either the loaded or mounted state.
    • The user modifies the source export, which makes the destination file mobility network unable to access the source file system.
• Protocol restrictions:
  • Import of SMB, multiprotocol settings, and related settings is not supported when performing an NFS-only import. These settings include settings for SMB server, SMB share path and options, Kerberos key, CAVA (Common AntiVirus Agent), usermapper, and ntxmap.
  • Import of a VDM using Secure NFS, NFSv4, or pNFS is not supported.
  • Import of FTP or SFTP (File Transfer Protocol), HTTP, or CEPP (Common Event Publishing Protocol) is not supported.
  • The NFS protocol is transparent, but sometimes client access behaviors can be impacted. Client access issues can arise from policy differences between the source VNX2 system and the destination PowerStore appliance.
    NOTE:NFSv3 I/O is transparent for SP failover and failback during the incremental copy stage. However, if failover or failback begins as the node is imported, an error may occur, disrupting client access and resulting in an I/O error. This error is resolved when the node is re-synchronized.

    NFSv3 operations such as CREATE, MKDIR, SYMLINK, MKNOD, REMOVE, RMDIR, RENAME, and LINK may fail with error during import cutover. For example, before cutover, an operation finishes successfully on the source VNX2 side. However, the client does not receive the response; after cutover, the client retries the same operation silently after cutover in an under layer.

    For example, if a file has already been removed on the source VNX2 side before cutover, the silent retry of the REMOVE operation fails with a NFS3ERR_NOENT message. You may see the remove failure even though the file has been removed on the file system. This failure notification occurs because after cutover, the XID cache that is used to detect duplicated requests does not exist on the destination PowerStore side. The duplicated request cannot be detected during cutover.

• Rollback restrictions and limitations:
  • After rollback, a host may need to remount the NFS file system if the interface configurations are different between the source VDMs and the destination NAS Servers.
  • Only rollback data changes to the source file systems are supported. Rollback of any configuration changes to the NAS server and file systems on the destination PowerStore appliance is not supported. For example, if you add an NFS export to a file system, a rollback does not add the new NFS export to the source VNX2 storage system.
• Configuration restrictions and limitations:
  • Import of NTP configuration is not supported.
  • Import of server parameter settings (VNX2 server_param settings except for the IP reflect parameter) is not supported.
  • Import of LDAP configuration with Kerberos authentication (SMB server is not imported) is not supported.
  • Import of client certificates, which the LDAP server requires (persona is not supported on the PowerStore appliance), is not supported.
  • Import of customized cipher list for LDAP connection (customized cipher list is not supported on the PowerStore appliance) is not supported.
  • If multiple LDAP servers are configured with different port numbers that are used by the source VDM, only the server with the port number equal to the first server is imported.
  • If both NIS and LDAP are configured and taken into effect for the naming service on the source VDM, you must select one of them to take effect on the destination NAS server.
  • If local files are configured and taken into effect for the naming service on the source VDM, you can select whether the local files take effect on the destination NAS server. The search order of the local files is always higher than NIS or LDAP on the destination NAS server.
  • Only enabled network interfaces on the source VDM are imported. Disabled network interfaces on the source VDM are not imported. (The destination system does not allow you to enable or disable network interfaces.)
  • FLR file systems can be imported on PowerStore appliances running operating system version 3.0 or later. However, PowerStore appliances with operating system versions earlier than 3.0 do not support file-based import and FLR.
  • Distributed Hierarchical Storage Management (DHSM)/(Cloud Tiering Appliance (CTA) may be configured on the source VNX2 for archiving inactive files to secondary storage. If DHSM/CTA is configured on the source VNX2 system and a VDM import to PowerStore is run, all the files on the associated file system are recalled from the secondary storage to the source VNX2. Those files are then imported to the PowerStore cluster as normal files (that is, no stub files are imported).
• Restoring NDMP backups:
  • The NDMP backup path on VNX2 is /root_vdm_xx/FSNAME while the same path on PowerStore is /FSNAME. If any file system of the source VNX2 VDM is protected by NDMP and already backed up, then after VDM file import, those file systems cannot be restored to PowerStore using the original path option. A restore using the original path option fails due to an unavailable destination path. Instead, use the alternative path option.