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Host Interconnect

Three types of host port connectivity are offered with a VTAng backup appliance:  SCSI and iSCSI and Fibre Channel.  The two Ultra 160 SCSI channels support both Single-Ended (SE) and Low-Voltage Differential (LVD) signalling.  High-Voltage Differential (HVD) signalling is also supported with the same software, but with a slightly different dual-channel SCSI card and device driver.  Standard Gigabit Ethernet (GbE) hardware may be used to provide iSCSI host connectivity.  Two GbE ports are typically available, and both can be used as iSCSI targets, or one can be used as an iSCSI target and the other as an iSCSI initiator (or regular TCP/IP network connection).  Fibre Channel connectivity is supplied with and embedded FC-to-SCSI storage router.  These host connectivity options give the customer the ability to use the VTAng backup appliance in both Direct-Attached Storage (DAS) and Storage Area Network (SAN) environments.  For example, a SCSI bus would typically be used for emulating DAS devices, and an iSCSI connection with an IP SAN.  With iSCSI, the backup appliance can be located further away from the host, facilitating off-site backups.  The customer gets to choose which host connectivity ports to use based on the particular environment and application requirements.

As described above, a single VTAng backup appliance provides two Ultra 160 SCSI Target Mode ports and two Ultra 160 SCSI Initiator Mode ports and the software that allows GbE ports to operate in iSCSI Target Mode.  Depending on how the system is configured, up to 30 virtual tape drives may be defined by the user, with all 30 of them accessible over the two SCSI channels, or with all 30 of them available over one or two iSCSI (GbE) ports, or with 15 over SCSI and 15 over iSCSI.  In the latter configuration, one Ultra 160 SCSI Initiator port is available for connecting external disk or tape resources, including an automated tape library or autoloader.

Regardless of which communication method is used, SCSI or iSCSI, the main function of the VTAng software is to act like a tape drive while writing data to (and also reading it back from) a disk drive.  But there are some added capabilities that make this a bit of a crossover product, with attributes of both a "Backup Hardware" type of product and also a "Networking Equipment" product.  For example, the appliance is not limited to exporting just virtual tape drives over iSCSI.  Local disk resources can also be made available as iSCSI targets, making the VTAng appliance appear as an iSCSI bridge, or storage router.  Disk or tape (or even tape library) resources may be connected locally to the appliance with any major storage interface (SCSI / SATA / SAS / Fibre Channel / iSCSI / USB / 1394), and these devices may then be mapped as iSCSI devices and made available to hosts in an IP SAN as iSCSI target devices.  With the Fibre Channel version, the embedded FC-to-SCSI router can be used to attach other legacy SCSI devices, not just the Virtual Tape ports in the storage appliance.

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