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## 6. Boot Arguments for SCSI Peripherals.

This section contains the descriptions of the boot args that are used for passing information about the installed SCSI host adapters, and SCSI devices.

## 6.1 Arguments for Upper and Mid-level Drivers

The upper level drivers handle all things SCSI, regardless of whether they be disk, tape, or CD-ROM. The mid level drivers handle things like disks, CD-ROMs and tapes without getting into low level host adapter device driver specifics.

### Maximum Probed LUNs (`max_scsi_luns=')

Each SCSI device can have a number of `sub-devices' contained within itself. The most common example is any of the SCSI CD-ROMs that handle more than one disk at a time. Each CD is addressed as a `Logical Unit Number' (LUN) of that particular device. But most devices, such as hard disks, tape drives and such are only one device, and will be assigned to LUN zero.

The problem arises with single LUN devices with bad firmware. Some poorly designed SCSI devices (old and unfortunately new) can not handle being probed for LUNs not equal to zero. They will respond by locking up, and possibly taking the whole SCSI bus down with them.

The kernel has a configuration option that allows you to set the maximum number of probed LUNs. The default is to only probe LUN zero, to avoid the problem described above.

To specify the number of probed LUNs at boot, one enters `max_scsi_luns=n' as a boot arg, where n is a number between one and eight. To avoid problems as described above, one would use n=1 to avoid upsetting such broken devices

### SCSI Logging (`scsi_logging=')

Supplying a non-zero value to this boot argument turns on logging of all SCSI events (error, scan, mlqueue, mlcomplete, llqueue, llcomplete, hlqueue, hlcomplete). Note that better control of which events are logged can be obtained via the `/proc/scsi/scsi` interface if you aren't interested in the events that take place at boot before the `/proc/` filesystem is accessible.

### Parameters for the SCSI Tape Driver (`st=')

Some boot time configuration of the SCSI tape driver can be achieved by using the following:

            st=buf_size[,write_threshold[,max_bufs]]

The first two numbers are specified in units of kB. The default `buf_size` is 32kB, and the maximum size that can be specified is a ridiculous 16384kB. The `write_threshold` is the value at which the buffer is committed to tape, with a default value of 30kB. The maximum number of buffers varies with the number of drives detected, and has a default of two. An example usage would be:

            st=32,30,2

Full details can be found in the `README.st` file that is in the `scsi` directory of the kernel source tree.

## 6.2 Arguments for SCSI Host Adapter Drivers

These are arguments for low level SCSI host device drivers, and as such are typically only used by those that compile their own kernel with the SCSI driver built in. These people are advised to check the source for the latest list of options that can be supplied to their driver.

`aha152x=` Adaptec aha151x, aha152x, aic6260, aic6360, SB16-SCSI

`aha1542=` Adaptec aha1540, aha1542

`aic7xxx=` Adaptec aha274x, aha284x, aic7xxx

`advansys=` AdvanSys SCSI Host Adaptors

`in2000=` Always IN2000 Host Adaptor

`AM53C974=` AMD AM53C974 based hardware

`BusLogic=` ISA/PCI/EISA BusLogic SCSI Hosts

`eata=` EATA SCSI Cards

`tmc8xx=` Future Domain TMC-8xx, TMC-950

`fdomain=` Future Domain TMC-16xx, TMC-3260, AHA-2920

`ppa=` IOMEGA Parallel Port / ZIP drive

`ncr5380=` NCR5380 based controllers

`ncr53c400=` NCR53c400 based controllers

`ncr53c406a=` NCR53c406a based controllers

`pas16=` Pro Audio Spectrum

`st0x=` Seagate ST-0x

`t128=` Trantor T128

`u14-34f=` Ultrastor SCSI cards

`wd7000=` Western Digital WD7000 cards

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