What is a driver, device file, device path in netbackup

[vinod_k316]

Hello everyone,

                  What is a driver, device file, device path which creates which and the functioning associated with each one.I have read the admin guides but i couldn't keep my finger on it.Anyone could please help me understand the basics behind them.Thank you for your time

[revarooo]

This isn't a NetBackup question.

Google Device Driver

A device driver is a program that controls a particular type of device that is attached to your computer. There are device drivers for printers, displays, CD-ROM readers, diskette drives, and so on. When you buy an operating system, many device drivers are built into the product.

Google Device File

In Unix-like operating systems, a device file or special file is an interface for a device driver that appears in a file system as if it were an ordinary file. There are also special files in MS-DOS, OS/2, and Microsoft Windows

Google Device Path

http://wiki.phoenix.com/wiki/index.php/Device_Path

There you will find your answers

[pkjohnston]

It could be considered a NetBackup question if you're new to supporting UNIX/Linux media servers and you're tasked to configure tape robots, drives, libraries, VTLs, ...

The pointers above can help plenty, along with the NetBackup configuration guide.

The latest NetBackup Device Configuration Guide (v7.6) is here: http://www.symantec.com/business/support/index?page=content&id=DOC6468

The starting point for all recent NBU docs is here: http://www.symantec.com/business/support/index?page=content&id=DOC5332&nbplp

Alternatively, SORT is another handly place to find product guides: https://sort.symantec.com/documents

[Marianne]

I am with Martin on this one... all of those are OS-level terms. You need some sort of OS background to understand how to configure and use backup devices at OS level before adding them to NetBackup. The only OS where NBU adds its own drivers is Solaris where sg driver is used along with OS device names to detect and add devices in NBU. Read the Solaris chapter in Device Config Guide.

[vinod_k316]

Thank you everyone actually i am new to netbackup, i have basic understanding of those terms but with respect to netbackup (while configuring new devices) i am getting a bit confused.So while configuring a new robot what actually does a device file and device path refer to.My basic understanding which may be wrong is...a robot communicates with a system through a driver(in solaris NBU issues os commands to the robot using sg driver) and sg driver in return creates device files(i donno why they are created and what they are used for) that's it.I couldn't understand how the drive path is created and why is it needed for a robot to work.So could some throw some insight in to these topics will help me alot.Thank you :)

[Marianne]

Have you read through the Solaris chapter in Device Config Guide as suggested a couple of days ago?

[revarooo]

About the NetBackup sg driver

NetBackup provides its own SCSI pass-through driver to communicate with
SCSI-controlled robotic peripherals. This driver is called the SCSA (generic SCSI
pass-through driver), also referred to as the sg driver.

For full feature support, NetBackup requires the sg driver and SCSI pass-through
device paths.
Install the NetBackup sg driver on each Solaris NetBackup media server that hosts
tape devices. Each time you add or remove a device, you should reinstall the sg
driver again.
If you do not use a pass-through driver, performance suffers.

NetBackup uses the pass-through driver for the following:
¡ By avrd and robotic processes to scan drives.
¡ By NetBackup to position tapes by using the locate-block method.
¡ By NetBackup for SAN error recovery.
¡ By NetBackup for Quantum SDLT performance optimization.
¡ By NetBackup for SCSI reservations.
¡ By NetBackup device configuration to collect robot and drive information.
¡ To collect Tape Alert information from tape devices allowing support of functions
such as tape drive cleaning.
¡ For WORM tape support.
¡ Future NetBackup features and enhancements

http://www.symantec.com/business/support/index?page=content&id=DOC6468

Page 62 and 63

[jmontagu]

vinod:

It is important to understand that Netbackup is incapable of direct access to your hardware. It depends on the Operating System to perform read/write /load/unload/rewind functions. Therefore any drive/device/driver requirements will be dependent on the Operating System of the Robot Control Host. 

Troubleshooting hardware errors is much easier when you understand that if the Operating System cannot see the Robot, Netbackup will never see it.

The following documentation will assist in troubleshooting common drive errors:

http://www.symantec.com/docs/TECH226192

[vinod_k316]

Yes marianne i have read about sg.build and sg.install, i also understoood that executing sg.install creates the device files.What i didn't understand is why it creates the device files and what is the use of them and i also understood that operating system creates the device path but what it has to with the netbackup i didn't understand.So kindly explain them to me at your convenience.Thank you

[mph999]

99.9% true 

NBU does send some scsi commands direct to the drives via the pass thru driver (sg), in Solaris in particular this is our driver.

[mph999 · Accepted solution]

There are two paths to the drives in Unix/ Linux

Solaris for example ...

/dev/rmt/0cbn - the OS device path

/dev/st/xx - the pass thru path

Some scsi commands commands eg. rewind / fast forward can be sent via the device (os) path, pretty much the same as the unix mt commands (mt -f /dev/rmt/0cbn rew to rewind a tape for example).

Other scsi commands, such as 'test unit ready' used when mounting a tape, to discover when thedrive has got things sorted and is ready to read/ write cannot be sent via the os path, and therefore go via the sg, or pass thru path.

So sg issues, in solaris can be our fault.

In linux, the pass thru oath (also known as sg) belongs to the os, so pass thru issues are usually down the the os vendor to sort out.

Generally, the only pass thru issue you see these days are on solaris, and in 99.9% of cases, is fixed by rebuilding them.   Usually, new drives don't appear in scan / tpautoconf (these scsi commands go via the sg driver ) and is simply a config issue.

In fact, in 8 years, I don't remember a single time an sg issue has been anything other than a reconfig to fix.

[vinod_k316]

Thank u martin and everyone for ur replies :)