Drivers Zetera Scsi & Raid Devices For Sale
Drivers Zetera Scsi & Raid Devices List

The driver creates the directory /sys/class/scsitape and populates it with directories corresponding to the existing tape devices. There are autorewind and non-rewind entries for each mode. The names are stxy and nstxy, where x is the tape number and y a character corresponding to the mode (none, l, m, a).
This compact appliance utilizes Zetera’s Z-SAN technology which, since its launch back in 2005. Each client system needs a SCSI miniport driver, a filter driver which converts file system.

This file contains brief information about the SCSI tape driver.The driver is currently maintained by Kai Mäkisara (emailKai.Makisara@kolumbus.fi)

Last modified: Tue Feb 9 21:54:16 2016 by kai.makisara

The Iomega USB to SCSI Cable Driver is used to ensure that a compatible operating system will recognize the Iomega USB to SCSI Cable device when it is connected to it. This driver will also provide the communication avenue that will be used by the device it supports, the software application and the operating system.

Basics¶

The driver is generic, i.e., it does not contain any code tailoredto any specific tape drive. The tape parameters can be specified withone of the following three methods:

1. Each user can specify the tape parameters he/she wants to usedirectly with ioctls. This is administratively a very simple andflexible method and applicable to single-user workstations. However,in a multiuser environment the next user finds the tape parameters instate the previous user left them.

2. The system manager (root) can define default values for some tapeparameters, like block size and density using the MTSETDRVBUFFER ioctl.These parameters can be programmed to come into effect either when anew tape is loaded into the drive or if writing begins at thebeginning of the tape. The second method is applicable if the tapedrive performs auto-detection of the tape format well (like someQIC-drives). The result is that any tape can be read, writing can becontinued using existing format, and the default format is used ifthe tape is rewritten from the beginning (or a new tape is writtenfor the first time). The first method is applicable if the drivedoes not perform auto-detection well enough and there is a single“sensible” mode for the device. An example is a DAT drive that isused only in variable block mode (I don’t know if this is sensibleor not :-).

The user can override the parameters defined by the systemmanager. The changes persist until the defaults again come intoeffect.

3. By default, up to four modes can be defined and selected using the minornumber (bits 5 and 6). The number of modes can be changed by changingST_NBR_MODE_BITS in st.h. Mode 0 corresponds to the defaults discussedabove. Additional modes are dormant until they are defined by thesystem manager (root). When specification of a new mode is started,the configuration of mode 0 is used to provide a starting point fordefinition of the new mode.

Using the modes allows the system manager to give the users choicesover some of the buffering parameters not directly accessible to theusers (buffered and asynchronous writes). The modes also allow choicesbetween formats in multi-tape operations (the explicitly overriddenparameters are reset when a new tape is loaded).

If more than one mode is used, all modes should contain definitionsfor the same set of parameters.

Many Unices contain internal tables that associate different modes tosupported devices. The Linux SCSI tape driver does not contain suchtables (and will not do that in future). Instead of that, a utilityprogram can be made that fetches the inquiry data sent by the device,scans its database, and sets up the modes using the ioctls. Anotheralternative is to make a small script that uses mt to set the defaultstailored to the system.

The driver supports fixed and variable block size (within bufferlimits). Both the auto-rewind (minor equals device number) andnon-rewind devices (minor is 128 + device number) are implemented.

In variable block mode, the byte count in write() determines the sizeof the physical block on tape. When reading, the drive reads the nexttape block and returns to the user the data if the read() byte countis at least the block size. Otherwise, error ENOMEM is returned.

In fixed block mode, the data transfer between the drive and thedriver is in multiples of the block size. The write() byte count mustbe a multiple of the block size. This is not required when reading butmay be advisable for portability.

Support is provided for changing the tape partition and partitioningof the tape with one or two partitions. By default support forpartitioned tape is disabled for each driver and it can be enabledwith the ioctl MTSETDRVBUFFER.

By default the driver writes one filemark when the device is closed afterwriting and the last operation has been a write. Two filemarks can beoptionally written. In both cases end of data is signified byreturning zero bytes for two consecutive reads.

Writing filemarks without the immediate bit set in the SCSI command block actsas a synchronization point, i.e., all remaining data form the drive buffers iswritten to tape before the command returns. This makes sure that write errorsare caught at that point, but this takes time. In some applications, severalconsecutive files must be written fast. The MTWEOFI operation can be used towrite the filemarks without flushing the drive buffer. Writing filemark atclose() is always flushing the drive buffers. However, if the previousoperation is MTWEOFI, close() does not write a filemark. This can be used ifthe program wants to close/open the tape device between files and wants toskip waiting.

If rewind, offline, bsf, or seek is done and previous tape operation waswrite, a filemark is written before moving tape.

The compile options are defined in the file linux/drivers/scsi/st_options.h.

4. If the open option O_NONBLOCK is used, open succeeds even if thedrive is not ready. If O_NONBLOCK is not used, the driver waits forthe drive to become ready. If this does not happen in ST_BLOCK_SECONDSseconds, open fails with the errno value EIO. With O_NONBLOCK thedevice can be opened for writing even if there is a write protectedtape in the drive (commands trying to write something return error ifattempted).

Minor Numbers¶

The tape driver currently supports up to 2^17 drives if 4 modes foreach drive are used.

The minor numbers consist of the following bit fields:

The non-rewind bit is always bit 7 (the uppermost bit in the lowermostbyte). The bits defining the mode are below the non-rewind bit. Theremaining bits define the tape device number. This numbering isbackward compatible with the numbering used when the minor number wasonly 8 bits wide.

Sysfs Support¶

The driver creates the directory /sys/class/scsi_tape and populates it withdirectories corresponding to the existing tape devices. There are autorewindand non-rewind entries for each mode. The names are stxy and nstxy, where xis the tape number and y a character corresponding to the mode (none, l, m,a). For example, the directories for the first tape device are (assuming fourmodes): st0 nst0 st0l nst0l st0m nst0m st0a nst0a.

Each directory contains the entries: default_blksize default_compressiondefault_density defined dev device driver. The file ‘defined’ contains 1if the mode is defined and zero if not defined. The files ‘default_*’ containthe defaults set by the user. The value -1 means the default is not set. Thefile ‘dev’ contains the device numbers corresponding to this device. The links‘device’ and ‘driver’ point to the SCSI device and driver entries.

Each directory also contains the entry ‘options’ which shows the currentlyenabled driver and mode options. The value in the file is a bit mask where thebit definitions are the same as those used with MTSETDRVBUFFER in setting theoptions.

A link named ‘tape’ is made from the SCSI device directory to the classdirectory corresponding to the mode 0 auto-rewind device (e.g., st0).

Sysfs and Statistics for Tape Devices¶

The st driver maintains statistics for tape drives inside the sysfs filesystem.The following method can be used to locate the statistics that areavailable (assuming that sysfs is mounted at /sys):

Use opendir(3) on the directory /sys/class/scsi_tape
Use readdir(3) to read the directory contents
Use regcomp(3)/regexec(3) to match directory entries to the extendedre

Drivers Zetera SCSI & RAID Devices