NAME

ts − SCSI tape controller

SYNOPSIS

device ts0 at sec? doneq 20 req 20 bin 5 unit 0 target 4

DESCRIPTION

This device driver supports SCSI target adapters for streaming tape drives.  It supports up to four tapes per target adapter and a maximum of seven target adapters per SCED board. 

The standard device names begin with “rts” followed by a number representing the tape unit, that is, “rts0” through “rts7”.  The corresponding no-rewind device name is eight greater than the standard name, that is, “rts8” through “rts15”. 

IMPLICATIONS OF STREAMING

Because the ts driver supports streaming tapes, the interface to the ts driver is different from that of “standard” tape drives, in these ways:

Block interface
The block interface is not supported at all.  Attempts to use it will return ENXIO.

Raw interface
The raw ts interface has several differences from standard tape:

To provide reasonable performance and drive life, transfers to and from the tape must be done in large chunks.  The ts driver assures this by buffering data internally.  One consequence of this is that errors on writes often cannot be reported until sometime long after the user passed that data to the driver.  Write errors will be reported to the user program on the next write system call after the error occurred, or on the close system call following the error. 

The raw interface does not support block sizes in the same fashion that standard tape does.  The ts tape device has a 512-byte physical block size.  User records are packed into these physical blocks on write and unpacked from these blocks on read.  So, when reading, the user gets as many bytes as he asks for, until end-of-file is encountered.  If less than a multiple of 512 bytes was written, the file size will be rounded up to a multiple of 512 bytes.  The extra bytes contain zeros. 

Reading part-way into a file on the no-rewind device, closing the device, and re-opening it will not work as expected.  The tape will always space forward to the beginning of the next file on close. 

IOCTLs

A subset of the ioctl functions are supported at this time.  Here is a list of supported and non-supported functions:

MTFSFis supported.(mt fsf nn)
MTWEOFis supported.(mt weof nn)
MTFSRis not supported.
MTBSRis not supported.
MTSEODis supported.(mt eod)
MTREWis supported.(mt rewind)
MTERASEis supported.(mt erase)
MTOFFLis not supported.
MTBSFis not supported.
MTRETis supported.(mt retension)

The MTERASE ioctl erases the entire tape and then rewinds it.  Reading status (mt status) is not supported. 

Ioctls will not always behave as expected if they are intermixed with reads and writes in a program. 

OPERATIONAL INFORMATION

A tape is always retensioned when it is first opened for read or ioctl.  It is erased when it is first opened for write.  Note that if the first operation performed on the tape after insertion (or booting) is “mt retension”, the tape will be retensioned twice.  This automatic retensioning of the tape is to help insure good data transfer, especially on writes to the tape. 

The data capacity of a tape will decrease with the number of soft errors on the tape and the number of times the drive must reposition between writes to the tape.  These consume tape space.  A reasonable expectation for a 450-foot tape is about 44 Mbytes. 

The mean time between failure of the tape drive is also affected by the number of repositions while reading or writing the tape.  The tape drive will “stream” better when it is accessed under light system load. 

CONFIGURATION

The “tsbconf” array in the device driver binary configuration file (/sys/conf/conf_ts.c) must contain an entry for each drive that may be configured; the entries must be in the same order as the “device” entries in the kernel configuration file (kernel configuration files are described in the article “Building DYNIX Systems with Config” in Volume 2).  As installed, “tsbconf” has entries for 4 drives.  Superfluous entries are ignored.

TUNING PARAMETERS

The following tuning parameters are defined for each drive in the “tsbconf” array of the binary configuration file:

(1)The buffer size (in k bytes) used to buffer data for I/O transfers.  Two buffers, each ofthis size, are allocated from the kernel’s free page pool when the device is opened.  These buffers are used to improve tape streaming performance.  The buffer space is released when the device is closed. 

(2)Flags for configurable features.  Flags available are:

TSC_OPENFAIL
When this flag is set, open calls to this device can fail for lack of physical memory for the buffers.   When this flag is clear, the buffer memory will always be allocated, but the process may block during this allocation process while other processes are swapped out to free up memory.

TSC_AUTORET
When this flag is set, the device will retension automatically on the first access after the tape has been changed.  When clear, it will not retension automatically.

TSC_PRSENSE
When this flag is set, all SCSI request sense buffers will be printed out, along with the command which caused the sense condition.  Otherwise, only sense buffers which are in some way unusual will be printed out.

(3)bits:  For the ADSI and Emulex target adapters, this should always be a 1 for proper operation of the device. 

FILES

/dev/rts∗ raw files

/sys/conf/conf_ts.c binary configuration file

SEE ALSO

mt(1), mtio(4), sd(4)

DIAGNOSTICS

ts: error writing buffer to tape.  An I/O error has occurred while writing the data to tape. 

ts: tsclose: error writing file mark on close.  An I/O error has occurred while writing a file mark to the tape.  This message often occurs following the previous message. 

ts: illegal read after write.  The process attempted to read data on the tape after successfully completing a write to the tape, without rewinding or retensioning the tape first. 

ts: tsioctl: bad operation after write.  The process attempted to issue an invalid ioctl after successfully completing a write to the tape.  Only rewinding and retensioning are valid after a write. 

ts: error on command command .  Many error messages take this form.  Error is one of:

Aborted command
Hardware error
Illegal request
Media error
Media is protected
Tape not ready
Unknown error
Vendor unique error
Volume overflow

Command is one of:

erase
mode select
read
request sense
retension
rewind
space
test unit ready
write
write file marks

Some error messages are accompanied by a display of the command buffer and the sense data buffer at the time of the error. 

BUGS

The double file mark at the end of the tape cannot be supported. 

DYNIX