Pass-through Disks

In this topic:

Resizing the source of a pass-through disk

About Pass-through Disks

A pass-through disk is the term used to identify a physical disk that is not a member of a pool, but is used as a storage source in a virtual disk. Pass-through disks are previously used physical disks with an existing file system and disk format (such as Windows, UNIX, AIX, Linux, Solaris, HP).software can migrate these disks into the configuration without modifying the structure of the existing data.

Pass-through disks can be used to create single, dual, or mirrored virtual disks. See Creating Virtual Disks for instructions on creating a virtual disk with a pass-through disk. For more information on how pass-through disks can be created from shared physical disks, see Shared Multi-port Array Support.

Using Pass-through Disks to Migrate Data

Pass-through disks are most often used as a temporary measure to migrate data.

Data is migrated from the existing storage architecture into SANsymphony™ Software-defined Storage platform to benefit from our storage services and management
Data is migrated from the existing storage architecture to a new storage architecture

Additional Benefits of Pass-through Disks

Data migration occurs with minimal disruption to current operations. Hosts can maintain access to current disk contents while the existing data is transferred to mirrored virtual disks.
Data migration occurs risk-free without requiring a backup/restore operation.
Features such as caching, replication over IP, mirroring, and snapshot operations can be performed on existing data during the migration process.

To illustrate how pass-through disks can be used, two common applications are described in the following paragraphs.

A mirrored virtual disk can be created using the pass-through disk from one server and adding a mirror from the pool of another server. The virtual disk created from the pass-through disk can be served to hosts and accessed while the existing data is being mirrored. When the mirror has been synchronized and the mirror recovery is complete, the pass-through disk is no longer needed. Although it is not required to do so, the pass-through disk can be removed from the virtual disk and replaced by a storage source from another pool.

SANsymphony software can be used as a vehicle to migrate data from one physical storage environment to another. In this scenario, the "existing" storage devices are connected to one DataCore Server and the "new" storage devices are connected to a partnered DataCore Server in the same server group. Mirrored virtual disks are created using the disks from the "existing" storage and the disks from the "new" storage devices. When the mirror recovery is complete, the data contained on both "existing" and "new" storage devices will be identical. The virtual disks can be split and the original physical storage devices can be removed. If SANsymphony™ Software-defined Storage platformwas used solely as a migration vehicle, then the SANsymphony software can be removed.

Important Notes:

The sector size of a pass-through disk must match the sector size of the virtual disk in which it is used as a storage source.
When a virtual disk created from a pass-through disk is deleted, this operation does not delete the data on the pass-through disk.
In a mirrored virtual disk, data on the preferred side is mirrored to the alternate side. To ensure that a pass-through disk is not overwritten by the mirroring process, the pass-through disk must be the first storage source selected when the virtual disk is created. Another way to easily ensure that data is not overwritten is to create a single virtual disk using the pass-through disk, then add a mirror later.
When creating virtual disks from pass-through disks for the purpose of migrating storage, remember that a pass-through disk cannot have a virtual disk already created from it in order to be included in the list of potential storage sources when creating virtual disks. A mirror (using a pass-through disk) can be added to a single virtual disk (created from a pass-through) as long as the mirror does not have a virtual disk created from it.
When using pass-through disks for the purpose of migrating or mirroring data, the DataCore Server has to have exclusive access to the pass-through disks and no other applications (for example Microsoft Cluster Services or VMware ESX machines) should share the disk. Another application writing to the pass-through disk during data migration can result in data corruption.
Creating pass-through virtual disks from pass-through physical disks consumes license capacity, increasing the amounts of current managed capacity and capacity license in use displayed in Server Group Details page>License tab.
See Creating Virtual Disks for instructions on creating a virtual disk with a pass-through disk.

Resizing the Source of a Pass-through Disk

To resize the source of a pass-through disk used in a virtual disk:

Unserve the virtual disk from the host. Before doing this, make a note of the LUNs used to serve the virtual disk to the host.
On the host, rescan or perform equivalent actions to ensure that the disk is no longer seen by the host.
Delete the virtual disk. Deleting the virtual disk does not delete the data on the physical disk.
Change the size of the physical disk at the storage level.
Make any amendments to the partition. For example, use Windows Disk Management to increase the size of an NTFS disk.
Create a new virtual disk using this physical disk as the source.
Serve the virtual disk to the host again using the same LUNs.