[BBLISA] Why do Linux rescue CDs make SATA disks look like SCSI ?

[John Stoffel]

>>>>> "David" == David Allan <dave at dpallan.com> writes:

David> On Thu, 15 Jan 2009, Brian McAllister wrote:
>> > The change causing non-SCSI disks to appear as sdX rather than hdX is not
>> > distro specific, it's a base kernel change.  With very new kernels, both
>> > IDE and SATA appear as SCSI disks.  There is some information available
>> > online as to why this change was made.
>> 
>> Clearly one can choose to use the old driver in a new kernel.  Is it
>> possible to build a kernel that has both drivers available as modules and
>> select which one to use at boot time ?

David> I don't know the answer to that; I'd guess it depends on the particular 
David> kernel version.

Well, if you roll your own rescue disk, you can build one kernel image
with the old IDE drivers (hdx) and one image with the newer 2.6 kernel
lib-ata drivers (sdx) for use on your hardware.

The basic issue is that as SATA drives started to become more
prevalent, the kernel guys (Jeff Garzik, Tejun, Bart...) started to
write a new driver core framework for the SATA interface, because it
offered a clean break withthe old IDE drivers which didn't support
newer features, sizes, performance, etc.

They then back ported in support for older IDE controllers, or mixed
SATA/IDE cards using ther libata framework.  They also decided to use
the SCSI mid-level to help abstract out disk access, and since the
SCSI mid-level was already very well supperted and understood, it made
snese to re-use that code.


Now in your case, you want to boot a RH7.3 system, using the hdX drive
names, using a much newer RHEL4 rescue disk, for access to newer
tools.  In this case, I think you can pass in an arguement on the
kernel boot stanza to tell it which drivers to use by default.

But in your case, since you're running such an old OS (I've still got
some systems running this too...) you might be better off using the
RH7.3 resuce disk.

I'd also recommend that you try to move any data on this hardware/OS
combo onto stable remote storage, so that yo ucan just re-install the
OS when you need to and not worry as much about ther data.

John