Specifications

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VMware GSX Server Virtual Machine Guide
host and you try to boot that disk inside a virtual machine, the boot program can fail if
the host geometry does not match the geometry used by the BusLogic virtual SCSI
adapter. The symptoms are that you see the first part of the boot loader — possibly an
LI from LILO, for example — but then the boot either stops or crashes.
BusLogic uses the following rules for generating disk geometries:
In each case the number of cylinders is calculated by taking the total capacity of the
disk and dividing by (heads*sectors). Fortunately, for sufficiently big disks, practically
all vendors use 255 heads and 63 sectors.
Drivers
In contrast to IDE adapters, SCSI adapters are not interchangeable and cannot all use
the same drivers. That is, if you have an Adaptec SCSI host adapter in your machine
and you remove it and replace it with a BusLogic SCSI host adapter, your operating
system is likely not to boot unless you install a BusLogic driver.
Dual booting from a disk that is also used as a virtual disk is no different. To your
operating system, it appears that the SCSI card in the machine suddenly changed
from whatever you own to a BusLogic card, and your operating system needs to have
a valid BusLogic driver installed. If that driver is not installed, you get a panic, a blue
screen or some similar fatal error as soon as the boot process tries to switch from the
BIOS bootstrap to the disk driver installed in the operating system.
Operating System Configuration
Many operating systems have configuration information that is different for SCSI and
IDE drives. For example, Linux uses /dev/hd[x] as the device name for IDE disks
and /dev/sd[x] for SCSI disks. References to these names appear in
/etc/fstab and other configuration files.
This is one reason that booting a raw IDE disk as a SCSI disk or vice versa does not work
well (if at all).
However, even when you are dealing only with SCSI devices, it is possible for an
operating system to encode information in a way that causes problems when you are
dual booting. For example, Solaris names its SCSI disks /dev/c[x]t[y]d[z]s0,
where the y represents the SCSI ID. So if you had a physical disk configured as SCSI ID
Disk size Heads Sectors
<= 1GB 64 32
> 1GB and <= 2GB 128 32
> 2GB 255 63