GridStor® (Alternate Data Paths) - Frequently Asked Questions
- Is Job Preemption supported for jobs with Storage Policy Copies that have Alternate Data Paths configured?
- Can I perform Change Data Path on Storage Policies with Storage Policy Copies that have Alternate Data Paths?
- How does Storage Policy Copies with Alternate Data Paths work in a clustered environment?
- How can I configure jobs that are run using data paths with Round Robin between HBA Cards?
- What happens when a storage policy is configured for multiplexing and contains data paths to be used in round-robin fashion?
- How does the failover to alternate data paths occur for jobs with multiple streams?
- How does backup use Alternate Data Paths?
- How does a restore operation use Alternate Data Paths when media are not available in a library?
Is Job Preemption supported for jobs with Storage Policy Copies that have Alternate Data Paths configured?
Job Preemption is supported for backups if the storage policy copies have the User Preferred Data Path or the Use Alternate Data Paths options configured. It is not supported for the jobs that are run using data paths with the Round Robin configuration.
Can I perform Change Data Path on Storage Policies with Storage Policy Copies that have Alternate Data Paths?
Change Data Path (right-click option) should not be performed on Storage Policies with Storage Policy Copies that have Alternate Data Paths (GridStor). If Change Data Path is performed on such a setup, data recovery operations can be performed from the media. However, subsequent data protection operations will not re-use the migrated media.
On clustered computers, the system automatically performs LAN-free operations for Agents that are installed on the virtual machines with the storage policy copy (attached to the subclient) pointing to the MediaAgent on the physical node. Consider the following example:
A file system iDataAgent is installed on Virtual Machine (VM1) and can be controlled by Node 1 or Node 2 at any given time.
The subclient (subclient1) associated with this file system iDataAgent on VM1 points to a Storage Policy Copy (SP1), which in turn uses the following data paths:
- default data path using MediaAgent (Node1) and Library 1
- alternate data path MediaAgent (Node2) and Library 1
When a backup is run on subclient1, the system automatically figures out the node controlling VM1 and will use the appropriate MediaAgent. For example if VM1 is controlled by Node 2 at the time of the backup, the system automatically uses the MediaAgent on Node2 to perform the LAN free backup.
This capability allows you to install the MediaAgent on the physical node of a cluster. (Instead of multiple instances if installed in the cluster group.) However, you will need GridStor® to provide failover capabilities.
When the devices are configured from different HBA cards on the same host as distinct drive pools, each of these drive pools can be added as data paths on the storage policy. For LAN storage policies, these data paths can be added as additional data paths with the Round-Robin between Data Paths option enabled. This will automatically round robin the data protection jobs between these HBA cards.
For LAN free Storage Policies, the additional LAN free data paths for the secondary HBA cards can be added as data paths and the software will automatically pick the least used LAN free data path.
(See Configuring Dual Host Bus Adaptors (HBA) for information on configuring HBA cards.)
What happens when a storage policy is configured for multiplexing and contains data paths to be used in round-robin fashion?
When a storage policy is configured for multiplexing and contains data paths to be used in round-robin fashion, then the round-robin option is completely utilized before using multiplexing.
For example, consider a storage policy with 3 data paths configured in the round robin mode and multiplexing set to 2. If 4 backup jobs kick off simultaneously, then the three available data paths are utilized first and multiplexing is applied for the fourth job only.
For multi-stream jobs, the failover will occur only when all the streams have the necessary resources. For example, if you have a job with 5-streams, and if the necessary resources are not available in the default data path, the failover will occur only when the alternate data path has all the necessary resources - MediaAgent, Library and drive pool with 5 drives. This is the case, irrespective of the criteria (When resources are busy, Round Robin between Data Paths options) specified to use alternate data paths.
When a backup operation is initiated, the storage policy copy attempts to write the data using the default data path. If the default data path is not available, an alternate data path is automatically used to perform the backup operation. If more than one alternate data path is defined, the first data path listed in the Data Paths tab of the Copy Properties dialog box is selected, followed by the second and so on until a data path is available.
Data can be restored/recovered from any compatible library and drive type in the CommCell.
When a restore operation is initiated, and if the media is not exported, the software attempts to restore/recover data using the appropriate data path associated with that library, instead of the default data path in the following order:
- The first priority is provided to the path which results in LAN-free restore/recover to the client computer from which the restore/recover operation was initiated. LAN-free operation is possible only when the client initiating the restore/recover operation and MediaAgent are on the same computer.
- If the LAN-free operation is not possible, then the restore operation attempts to restore/recover data using the default data path.
- If the appropriate media is not available in all these data paths, the software automatically identifies the media in which the data resides and performs the restore/recover operation from that library.