TAPE DEVICES and RESTORE METHODS

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Device Types RESTORE Mechanisms
Device Flags Tape Troubleshooting

Device Types

jBASE provides support for the following tape devices. The device control records are located in the ‘dev’ subdirectory of the jBASE release directory.

FLOPPY - Floppy disc. Usually blocked at 500 bytes with 12 byte header.

SCT - Streaming cartridge tape. Usually blocked at 8192. 512 fixed byte blks.

DAT - 4mm cartridge tapes. Usually blocked at 16384. Variable length.

HALF - Half inch tape. Usually blocked at 16384. Variable length.

FILE - Unix or NT file requires additional path parameter.

The actual tape device files on Unix reside in the ‘/dev/rmt’ directory, however naming conventions differ between the various different platforms.The actual tape devices on NT are named by convention \.\TAPE0, etc. Where as the floppy disc is named as \\.\A:

 Note: Windows 95 does not support tape devices via the Win32 standard interface. However jBASE has been enabled to read and write to the Win95 floppy disc drive.

Compression and formats can vary between different manufacturers of the same device. When reading or writing a tape ensure that the target system device is compatible with the format of the written media.

QIC 150 and QIC 525 appear to be readable by most Stream cartridge tape drives. In general higher specification drives tend to be able to read, but not necessarily write, lower specification media tapes.

Note: Some DAT devices must be enabled for variable length blocks before they can be read else they produce no data status. This can also happen when the requested block size is lower than the actual block size on tape.

To enable variable length tape on SVR4 systems use the following command.

tapecntl -v /dev/rmt/devicename

On AIX use ‘smitty’ to set tape device for variable length.

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Device Flags

-D DeviceName - Device to open in no rewind mode.

-I LockId - Lock name for T-ATT to show device attached.

 -M MediaType - Media name. SCT, DAT, HALF, FLOPPY, FILE.

-L Type,Size - Label Type and expected size e.g. R83,8192 or ROS,80

-T TTYName - Alternative device for next reel prompt or errors etc.

-S SizeKb - Max size of device. Floppy only

-H HeaderSize - Specifies bytes to skip for each block.

-R DeviceName - Device for rewind mode

-P PadChar - Value of -1 No pad on WRITET, -P0xff pads with 0xff.

-B Blocksize - Default block size to read and write.

The Label and block size parameters can be overridden from the T-ATT command line. For instance to attach and read a tape blocked at 5120, i.e. a tar, use the following command.

T-ATT SCT0 SIZE=5120 LABEL=0

To read a tape produced by R83 use the following command.

T-ATT DAT0 SIZE=16384 LABEL=R83,-2

The -2 means the label is expected to be the same block size as the other tape blocks. To read a tape produced by a ROS system use the following command.

T-ATT DAT0 SIZE=16384 LABEL=ROS,80

Note: Streaming cartridge drives automatically pad to 512 byte boundary on write. So tapes written at block sizes not divisible by 512, e.g. 8000, cannot easily be copied to a file, as the padding will become part of the data when read via the FILE option. This is not a problem if reading from the QIC device as the driver will always read in blocks at multiples of 512. And then attempt to use the labeled block size for data retrieval.

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RESTORE Mechanisms

T-LOAD

The jBASE T-LOAD utility can be used to load individual files saved in standard SMA T-DUMP format. However care should be taken when generating a T-DUMP tape as binary records are not covered by the T-DUMP standard and as such various vendors have used their own format.

ACCOUNT-RESTORE

The jBASE ACCOUNT-RESTORE utility can be used to load individual accounts from most vendor ACCOUNT-SAVE formats. The utility has been specifically constructed to cater for the majority of vendor specific formats, where divergence from the SMA standards usually occur, such as in the handling of binary or large data records. 

SYSRESTORE

The jBASE SYSRESTORE utility can be used to load multiple accounts from most vendor FILE-SAVE formats, although in some cases the ACCOUNT-RESTORE utility may provide better control of the data/accounts restored.

MAGRES

The jBASE MAGRES utility can be used to restore multiple accounts from a MAGSAVE formatted save. The utility restores all files into their respective directories.

RESUV

The jBASE RESUV utility can be used to restore multiple accounts from a UVBACKUP formatted save. The utility by default restores all the files to their respective directories, then removes empty redundant files, then resizes the files and finally automatically executes the Portbas utility for the detected source files

RESTOREADDS

The jBASE RESTOREADDS utility can be used to restore floppy disks saved in the ACCOUNT-SAVE format from an ADDS MENTOR systems. The reason for standard ACCOUNT-RESTORE utility cannot be used is because the floppy disk contains a two dummy blocks, one at the start and one at the end of the floppy. The dummy block at the end of the floppy is the main problem as the tape driver cannot determine that this dummy block is not good data.

Note:

UNIDATA provide a save format called ACCSAVE but it is effectively a cpio and thus is not portable. These tape formats cannot be used for restore. Even UNIDATA have to run a byte switching operation after files have been restored from different endian machines.

i.e. Risc Machines Big Endian v Intel Machines Little Endian.

Big Endian means that a 4 byte int x"12345678" appears in memory as a consecutive sequence.

Little Endian means that the 4 bytes are swapped so it appears as the sequence x"78563412".

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