Disk Bridge or Virtual disks

Description

This article describes the two shared storage creation options available in StarWind Virtual SAN: Disk Bridge and Virtual Disks. Disk Bridge provides full SCSI layer emulation, allowing existing physical storage devices to be exported directly to remote initiator clients. This includes hard drives, optical devices, and other physical storage hardware, enabling clients to work with the exported devices as if they were locally attached.

Virtual Disks are created using Image File technology, where a virtual iSCSI hard drive is stored as a regular disk file containing a raw set of sectors. Clients connect to these virtual disks as to physical drives, allowing standard formatting and data storage. The article outlines architectural differences, supported capabilities, and limitations of each option to help administrators select the appropriate storage type.

Background

StarWind Virtual SAN™ offers two options to create the shared storage:

• Disk Bridge. The Disk Bridge module provides complete emulation of the SCSI layer that enables remote initiator clients to use any type of hard drive (PATA/SATA/RAID).

Using the SPTI (SCSI Pass Through Interface) module (similar to RDM physical compatibility mode) you can export any other physical storage device, including optical devices that are attached to the computer (CD, DVD, Blu-ray, and HD-DVD, including burners), magneto-optical devices (ATAPI, USB, or FireWire are supported), physical tape drives, changers, etc.

Users connected to exported devices are able to store data, burn to remote burners, create remote backups and so on.

• Virtual Disks. The Image File technology allows for the creation of virtual iSCSI hard drives within a regular disk file.
  The file is a RAW set of sectors of the virtual hard drive. Clients connect to the image file device as if it were a local physical drive. They can format it in the usual way and store data on it.

Main guidelines

When choosing between the mentioned above one must consider those differences:
· Virtual Disk allows creation of multiple LUNs on top of single hard drive. Meanwhile, Disk Bridge works only on 1 LUN per 1 Hard Drive basis.
· If the SCSI path is changed for any reason on the RAID controller, that will make the Disk Bridge-based LUN to become not active. That will never happen with a Virtual Disk-based LUN.
· Disk Bridge doesn`t include Deduplication functionality
· Disk Bridge doesn`t support StarWind side Snapshots
· Disk Bridge doesn`t support automated snapshot tiering

Conclusion

Disk Bridge is intended for scenarios where an existing physical disk with a required file system must be exported directly to a client or application. In all other cases, StarWind officially recommends using Virtual Disks, as they provide a more flexible and reliable approach to shared storage creation.