Concepts of tape virtualization
Virtualization helps make full use of modern tape storage capacity and reduces the access time for storing and retrieving data. Instead of using physical tape drives and libraries, the system uses virtual devices that look and behave the same to applications.
Inside a TS7785 system
The TS7785 uses disk drive modules (DDMs) for storage and emulates IBM LTO-5 tape drives. To your applications, these virtual drives look and act just like physical tape drives. Virtualization does not change how applications use tape, allowing existing tape-based workflows to continue without modification.
Virtual tape libraries (VTLs)
A virtual tape library (VTL) instance is an emulated tape library in the IBM TS7785 grid. In the current release, the only supported virtual library type is an emulated IBM TS4500 tape library. Each VTL looks like a physical tape library to backup or host applications and presents standard tape library elements such as drives, slots, and cartridges.
You can create multiple VTLs to align with different application needs, business units, or service tiers. A TS7785 supports up to four virtual tape library instances.
Supported host applications
A VTL supports host application types such as IBM i and IBM Storage Protect. From the host perspective, the virtual library appears as a standard tape library. Hosts see standard tape library elements, including drives, slots, and cartridges, and can interact with them using normal tape operations.
Virtual tape drives
A virtual tape drive is an emulated tape drive within a virtual tape library. The TS7785 emulates IBM LTO-5 tape drives, and applications can mount, read, and write to those drives in the same way they would with physical tape drives. The TS7785 uses disk to serve these operations at high speed.
A virtual tape drive belongs to a specific virtual tape library. During library creation, you define the number of virtual tape drives per cluster, and each drive is accessible through one cluster in the grid. The drives that are created are evenly distributed across all clusters in the grid.
Each virtual tape drive has:
- A serial number, which is automatically created by the grid when the drive is created
- A device ID, which is the SCSI device ID of the tape drive
Add more virtual drives to increase parallelism and throughput. Size drive counts and schedules to meet your backup window.
Virtual device exposure and limits
Virtual devices are configured within the clusters and exposed to host applications through host mappings. To allow hosts to access virtual tape devices, you create a host group, define the host and host port information, select the virtual tape drives that the hosts can access, and then define the set of virtual library ports through which the hosts can access those drives.
The system supports up to 512 virtual tape devices per cluster.
Virtual tape cartridges
A virtual tape cartridge is a virtual tape volume that stores data on the TS7785's disk-based storage. When data is written or read, it is stored in a virtual cartridge on the disk drive modules (DDMs) in the TS7785 cluster.
Virtual cartridges behave like physical tape volumes, but they use only as much space as needed for the data stored. This makes storage more efficient and helps make better use of the underlying physical storage.
The currently supported cartridge type is LTO-5, with 500 GB of native capacity.
VOLSER and VOLSER ranges
A VOLSER (volume serial number) is the serial number that identifies a cartridge. In physical cartridges, this is the barcode printed on the cartridge label. A VOLSER is six characters in length, using A–Z and 0–9, plus two characters that identify the cartridge type. A VOLSER range is a range of these cartridge identifiers.
Cartridge pools
A cartridge pool is a set of virtual cartridges that share a common set of behavior settings. The cartridge pool defines cartridge behavior for:
- Replication settings, such as local copy only, copy everywhere, paired copy, one copy per region, or custom replication
- Cloud tiering settings, such as cloud repositories, copy delay, and grid retention
- Data settings, such as cartridge capacity, compression method, and WORM settings
When you create a virtual library, you define the set of virtual tape cartridges that will be available to all clusters in the grid. During library creation, the system validates the library configuration, checks for naming conflicts, allocates resources from the available cartridge pools, creates the virtual library object in the grid database, and displays the new virtual library in the libraries list. Pool settings can be updated later, and more cartridges can be added after the library is created.
Virtual slots
Virtual slots are the slot locations within the virtual tape library. These include:
- Storage slots – Hold cartridges within the library
- Import/export slots (also called cartridge I/O slots) – The virtual representation of the I/O slots where cartridges are inserted into or removed from the library
These slots are part of the standard tape library elements that hosts see when they connect to a VTL. Because the virtual library is presented as an emulated physical tape library, hosts see these slot types as part of the library structure.
Media changer device
A media changer device is a device that represents the library or robot where SCSI mount and demount commands are sent. It is part of the virtual tape library environment that is presented to the host.
The media changer device is exposed to the host through device mappings and accessed through the configured virtual port mappings. Device mappings are the set of tape drive and media changer devices that the hosts in a host group can send commands to.
Virtual ports
A virtual port is a port surfaced for the virtual library that a host can connect to in order to send commands to virtual tape drives or media changer devices. In a Fibre Channel environment, a virtual port appears with a World Wide Port Name (WWPN) that is zoned to host initiator ports.
Each cluster exposes multiple virtual ports for scale and resilience. Each virtual port is assigned to one cluster port, meaning that virtual ports are mapped one-to-one to cluster ports.
Host mapping
Map each host or host group to one or more virtual ports on a cluster. The mapping controls which VTLs, drives, and cartridges the host can see and the communication paths that are available.
To configure host access:
- Zone host initiator ports to the cluster's virtual ports
- Present the required VTLs and virtual drives to the host
- Use multiple paths per host for higher bandwidth and failover
Caching and copies
All data stays in virtual cartridges in the TS7785 cache. Smart caching keeps the most recent or frequently used data ready for quick access. Policies can influence what stays in the cache.
When a virtual cartridge is copied to another site over the grid network, it's called a copy.
