Introduction 

IBM Storage FlashSystem just announced new software version 8.7.3.0 which simplifies the mobility management of the storage partitions. Storage partition is a set of objects such as volumes, volume groups, hosts and host mappings required to handle enterprise workloads. The Storage partitions can also be viewed as a set of storage resources which can be easily moved across IBM FlashSystems ensuring no application downtimes. This blog explores how the latest software delivers easy and non-disruptive Storage Partition Migration experience by making use of host operating system specific capabilities of discovering the storage availability.

Storage Partition Migration in action^[1]

The Storage Partition migration flow automates various steps such as assigning replication policies, establishing Policy Based data replication configurations, and moving the partition data along with the corresponding objects to the Target FlashSystem. The following graphics provides an overview for the automatic movement of the storage controller resources during the migration process.

Host storage discovery capabilities

Host severs environments (such as ESX) have a peculiar, optimised behaviour of automatic storage scanning at regular intervals. This allows the host operating system to detect and act upon any config changes such as virtual volumes mappings or network zonings at the fabric or storage controllers. The new IBM FlashSystem software makes use of these host capabilities for an enhanced storage partition migration experience which minimises manual user interventions.

Enhancing Host Integration 
For environments with automatic rescan capabilities, the administrator for the Storage Partition does not need to go to every ESX host (or any other automated storage rescan capable environment) to trigger storage rescans which was a mandatory and time-consuming manual process prior to this release.

To improve the end-to-end user experience, the new software introduces a new set of features for making the most of host environment and storage detection capabilities -

- Detection of Automatic storage rescan capabilities of the mapped hosts: The new version detects if the operating system of the mapped host (such as ESX) is known to have characteristics of triggering storage rescans at regular time intervals. This insight gets internally used by the partition migration logic to avoid manual user interventions for the storage rescans from such capable hosts.
- Providing Host Insights: The new version introduces technology to derive statistics about the IO or discovery status using the SCSI exchange traffic with the host. This information is also now available in the host object view commands (such as lshost).
- Manual Configuration or Override Options: The storage administrator may configure automatic storage rescan behaviour using third party utilities in host operating systems which typically lack the auto rescan capabilities. In such cases, the administrators can manually configure ^[2][3] the host object so that the migration flow makes necessary adjustments and avoids manual storage rescans user interventions.

Making critical decisions is now easy

The most important and critical decision in the storage partition migration process is to provide consent to delete the source copy of the storage partition. The partition migration has multiple built in security checks during the migration process to ensure a smooth user experience.

To make the critical decision making easier, this new software version provides additional insights about how the hosts perceive the partition resources in transit. These insights are designed to help dealing with any instances of suboptimal storage performances, issues arising from host multipathing policies, incomplete host storage discoveries etc. The following host statistics are presented in a user consumable fix procedure in case any discrepancies are found during the migration phase:

• 
  - Total number of hosts : A quick overview of the complete host environment.
  - Status: Identifying the number of offline or degraded hosts.
  - Discoveries: Identifying the number of hosts which have successfully discovered the storage from the target FlashSystem.
  - I/O Activity: Whether any host has carried out I/O operations on source at time of switching the ownership of the storage partition to the desired target FlashSystem. A fix procedure indicates if there is any IO activity from the hosts to the source target FlashSystem within the last two minutes. This is a prior indication of how the host perceives the paths from the source and target FlashSystems and may help troubleshooting any config issues such as host multipathing policies or unavailability of highly available storage paths.

Conclusion 
The latest enhancements in Storage Partition Migration significantly improves ease of use and provide valuable host insights. These advancements empower users to make informed decisions and ensure a seamless, non-disruptive and efficient data mobility experience.

References

1. To understand Storage Partition Migration workflow, refer to:
Storage Partition Migration

2. To manually configure host rescan behaviour, refer to:
Configuration_of_host

3. To override rescan behaviour of host, refer to:
Override_rescan_behaviour_of_host

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