I have IDE 5 hard drives in a software RAID 5 array and one SATA drive containing my OS partitioned as follows:

/dev/sda1 /boot
/dev/sda2 swap
/dev/sda3 /
/dev/vg0/home /home
/dev/vg0/var /var

vg0 is the LVM volume group that spans the RAID5 array. there are other volumes not related to the OS in the array.

I have no difficulty installing grub from the grub shell with
>root hd(3,0)
>setup (hd3)

but when I reboot the computer, grub goes immediately to error 21 without presenting me a boot menu.

Any help would be greatly appreciated.

I do not use LVm but you have got a bootloader...grub on hd3 or your fourth detected drive.

is that what you want?

which drive does your bios order normally detect?

Normally you put grub onto hd0.

root (hd3,0)
setup (hd0)

I tried that and it gave me the same error, so I tried disconnecting the RAIDed drives and just booting the SATA drive. Now, I received error 15 instead of 21. After reinstalling grub with the IDE drives removed, I successfully booted the SATA drive. After plugging in the IDE drives however, error 21 returned. At this point, I changed the BIOS boot device from HDD0 to SCSI and now it is booting properly. After having this machine for two years, I only now just found out that not only Linux, but also the BIOS, treats SATA as SCSI.

well yes and no.

i have a single sata drive non-raided....but after a bios update...I needed to enable raid for the onboard raid to detect the sata drive.

you may want to check with your motherboard manufacturer for a bios update but be aware that flashing your bios may require a floppy drive?

Not sure years later I came across this post via google...

root (hd0,0) #This is boot partition
setup (hd0) #This is mbr watever that means
quit

Not sure bout LVM, thats what I was searching via google...still dont know what the hell that means..but im curios of the possibilities