Like virtual disks, virtual tape devices appear as files to the host system. By default, Avanti assigns the extension .vtape to a virtual tape file. The vtape format utilized by Avanti is fully compatible with the vtape format used in SimH. Avanti virtual tape devices default to a DEC DLT2000 device type.
Each SCSI tape READ or WRITE command may transfer at most 16 MiB. A larger request returns a SCSI error without allocating or transferring the requested data. This per-command limit does not limit the total size of a virtual tape file.
A single WRITE FILEMARKS command may write at most 1,024 marks. Issue additional commands for a larger sequence; the total number of marks on a virtual tape is not limited by this per-command bound.
SPACE to end-of-data is not supported and returns a SCSI check condition rather than repositioning the tape. A failure to finalize a tape image during UNLOAD also returns a check condition; do not replace the host file until Avanti has released it successfully.
Note:Avanti puts no limit on the size of a vtape file. Continuously appending to a tape will eventually fill the host system disk.
Avanti treats virtual tape files as follows:
•If a virtual tape file does not exist when Avanti opens the device, it is created.
•After the guest unloads the tape and the host file is renamed, Avanti creates a new tape file the next time the associated tape device is accessed. See Changing Tapes for the safe procedure.
•If a virtual tape file exists on Avanti startup, it is used.
•Avanti holds the tape file open with host read sharing only after the following operations. Windows processes may read or copy the file, but cannot write, rename, or delete it until the guest unloads the tape:
-Tru64: Tape read/write operations commence.
-VMS: Historical OpenVMS field guidance states that tape activity begins when INITIALIZE or MOUNT is executed and that an INITIALIZE'd backing file remains locked until a later MOUNT/DISMOUNT sequence or guest shutdown. This guest-command lifecycle has not been revalidated for Avanti 5.1.0.
•Avanti releases a tape file when an UNLOAD command is sent to the virtual tape drive. The following operations issue an UNLOAD command:
-Tru64: The mt unload and mt offline forms are retained historical command examples and have not been revalidated across the supported Tru64 releases. Verify the command accepted by the installed release.
-VMS: Historical OpenVMS field guidance states that DISMOUNT issues the UNLOAD command. This guest-to-SCSI behavior has not been revalidated for Avanti 5.1.0; confirm that Avanti has released the backing file before replacing or renaming it.
•Historical OpenVMS field reports state that INITIALIZE reduced the underlying tape file to a few kilobytes. This guest-specific result has not been revalidated for Avanti 5.1.0; the production implementation guarantees only that, after the current session records a write, closing or unloading truncates the backing file to the logical content length recorded during that session.
