Auto-generated Virtual Disks

In order to explain auto-generated virtual disks, a brief explanation of logical disks is required.  Logical disks are used internally by the software and are not revealed in the DataCore Management Console. A logical disk is a representation of a virtual disk on a server. Logical disks are created by the software when virtual disks are created from disk pools or pass-through disks. A single virtual disk is comprised of one logical disk from one server. A mirrored or dual virtual disk is comprised of two logical disks—one logical disk from each server that was used as a storage source for the virtual disk. Therefore, logical disks are most closely related to "storage sources" that are selected when a virtual disk is created in the console.

When a logical disk is detected by the software and a corresponding virtual disk (including rollbacks and snapshots) cannot be found, a message that the system will be creating the auto-generated virtual disks will appear on the screen. The user must click OK to proceed and the virtual disks will be created after a brief delay.

When possible the auto-generated virtual disk will have the same name and be the same size as the original virtual disk, however virtual disk SCSI Information is not retained. (This means the SCSI device Id on the auto-generated virtual disk will not be the same as it was on the original virtual disk, thus any host identifying a virtual disk by NAA / EUID may see the auto-generated virtual disk as a new device not previously discovered.) The description in the Virtual Disk Details page will read "This is an automatically generated virtual disk." When the logical disk properties cannot be found, auto-generated virtual disks are assigned default names beginning with "Auto Generated Virtual Disk 1" and have a default size of 2 TB.

Auto-generated virtual disks may also include snapshots, rollbacks, history logs, logstores, and mapstores.

Auto-generated virtual disks that are differential snapshots, rollbacks, logstores, mapstores, and history logs are invalid and should be deleted from the configuration to regain space in the pool. The validity of full snapshots depends on the state and circumstances of the storage sources.

Auto-generated virtual disks can be created under several different scenarios. These auto-generated virtual disks can either be used or deleted by the user based on the circumstances.

The servers must comply with the licensing for auto-generated disks to appear. This is especially applicable when importing a foreign pool that may place the server out of compliance. For example, when rebuilding a server without a configuration backup while using the trial license before activating the original license keys.

Some example scenarios:

• A foreign pool is imported from a different server. The software detects the logical disks created from the foreign pool, but cannot find corresponding virtual disks on that server, so auto-generated virtual disks are created. In this case, the auto-generated virtual disks could be served to a host and used as storage. (See Importing Foreign Pools.)
• A back-end physical disk fails in a disk pool resulting in failed virtual disks. The storage sources in the failed disk pool are in the process of being replaced with new storage sources from a healthy pool. During this operation, new logical disks are created. If the failed pool goes healthy during this process at a certain stage, the software will detect logical disks without the corresponding virtual disks on the server and auto-generated virtual disks will be created for the virtual disks that were replaced. In this case, the auto-generated virtual disks can be deleted (after verifying that the mirrors are up-to-date and healthy after the repair) in order to reclaim the space used in the disk pool. This scenario could also occur with the Split and Unserve operation or when repairing virtual disks in a failed pool by running the Windows PowerShell script file named "Repair-DcsVirtualDisk.ps1" which is included with the DataCore SANsymphony installation. (See Repairing Virtual Disks.)
• Virtual disks are deleted while a disk pool is unavailable or not healthy. If the unhealthy disk pool comes back online, the software will detect the logical disks from the formerly unhealthy pool and not find the corresponding virtual disks which were deleted. Auto-generated virtual disks will be created. In this case, these virtual disks can be deleted since they are no longer wanted and use disk pool resources.