System Boot Problems
9-2
Express5800/
ftServer
: System Administrator’s Guide for the Linux Operating System
Normal Boot Sequence
The active CPU-I/O enclosure (that is, the primary enclosure whose power switch is lit
green) initiates the boot by starting the BIOS. The BIOS on the booting enclosure scans
the list of bootable devices (as configured in the BIOS) looking for a device to boot.
When the search finds the disks, they are analyzed from bottom to top in the boot
enclosure. When a disk with a boot partition is found, it is booted.
The boot sequence is a multi-stage process:
•
The GRUB boot loader is loaded and started.
•
The GRUB boot loader loads the second stage GRUB, which selects the Linux
kernel to boot, loads, and starts it. The boot process uses the raw disk; RAID is not
involved.
N O T E
For the boot sequence to work, a bootable medium must
be found in the active CPU-I/O enclosure. For example, if
you try to boot the top CPU-I/O enclosure, the boot
sequence fails if sda is missing and there is no other
bootable disk. If a boot partition is found in sdb or sdc, it is
booted. If the boot fails, the system switches the active
CPU-I/O enclosure and tries again (where it will find and
boot sdd, if present).
•
When the kernel starts, it loads the SCSI driver, which in turn loads the
SAS (
SATA
)
driver.
•
The S
AS (S
ATA
)
driver spins up all the disks it discovers. It also collects a list of all of the
type 0xfd (Linux RAID autodetect) partitions.
•
When the RAID-1 module is loaded, it processes this list of mirrors and starts RAID
arrays. It processes mirrors from disks in the following order: sda, sdd, sdb, sde,
sdc, and sdf. If a RAID array was not cleanly shut down, a resync is started.
N O T E S
1. The RAID arrays that are started are started as
described above, regardless of what kernel was
booted (or which disk contained the kernel).
2. The recommended configuration of sda and sdd
system disks results in the expected boot
sequencing. The kernel is found in sda or sdd, and the
system file systems are also on sda and sdd.
•
Later in the boot sequence,
/etc/rc.sysinit
runs. It finds and starts any RAID
arrays in
/etc/mdadm.conf
that were not already started and that are required
by mounts in
/etc/fstab
.
