SCSI drivers that are built into the kernel are checked in a pre-determined order to see if HBAs that they can control are present. The user has no control over this order which in most cases is arbitrary but in the case of some older ISA adapters is required to stop misidentification  .
scsi_logging=<n> where <n> is 0 to turn logging off where <n> is non-zero to turn logging on max_scsi_luns=<n> where <n> is a number between 1 and 8 (< lk 2.4.7), >= lk 2.4.7 the upper limit can be much larger scsihosts=host0:hosts1::host3
The recently introduced devfs defines a "scsihosts" boot time parameter to give the user some control over this. See the devfs documentation [ref: W5] for a description. The host names given in the list to the "scsihosts" boot option are the names of lower level drivers (e.g. "scsihosts=advansys:imm::ide-scsi").   Devfs does not need to be present for "scsihosts" to be used. The "scsihosts" parameter, if given, is echoed during in the boot up messages. For example:
scsi: host order: advansys:imm::ide-scsi
A full list of kernel parameters with some explanations can be found in the file /usr/src/linux/Documentation/kernel-parameters.txt .
PCI adapters are much "safer" for initialization code than the older ISA adapters. Hence the order of initialization of PCI adapters is unlikely to lead to lockups. In this case the order of initialization (and thus SCSI adapter numbers) of built in drivers may be modified by changing the order of entries in the SCSI subsystem Makefile ( /usr/src/linux/drivers/scsi/Makefile). Beware: some adapters may be recognized by more than one lower level driver (e.g. those based on NCR chipsets).
Either comma or colon can be delimiters for "scsihosts". This means that "scsihosts=advansys,imm,,ide-scsi" is also valid.
Using "scsihosts" can lead to a situation in which the computer's BIOS finds the boot track (and hence boot time parameters set in lilo or grub) on one disk while the kernel finds the root partition on another disk. This can be quite confusing when it is unplanned. Hence after changing (or adding) "scsihosts" in lilo or grub's configuration, it may be wise to boot the machine to see which disks are accessed.