Use large disks on Cobalt Raq
SUN Sobalt Raq's (as far as I know about Raq 3 / Raq 4 / Raq 550) use IDE controllers with 24 bits for addressing. For example, Cobalt Raq 550 uses a Serverworks LBA24 controller.
24 bit addressing supports a maximum of ~137 GB harddrives. In order to use larger hard drives (>137 GB) a PCI expansion controller has to be installed using a RISER card in the Cobalt PCI slot.

In my Cobalt Raq 550, I installed an Adaptec 2610sa SATA controller using the Adaptec AACRaid driver. To make this controller work, include the driver into the Kernel. Use this guide to install a custom Kernel. At the make menuconfig part, go into the following menu and select these includes:

Device Drivers -->
<*> Serial ATA (prod) and Parallel ATA (experimental) drivers
[*] Multiple devices driver support (RAID and LVM)
Device Drivers --> Multiple devices driver support (RAID and LVM) -->
RAID support
Linear (append) mode
RAID-0 (striping) mode
RAID-1 (mirroring) mode
Device mapper support
Device Drivers --> SCSI device support --> SCSI low-level drivers -->
<*> Adaptec AACRAID support

The required driver might also be listed under one of the following menues:
Device Drivers --> ATA/ATAPI/MFM/RLL
Device Drivers --> Serial ATA (prod) and Partallel ATA (experimental) drivers
(See for example)

After that, proceed with:

make-kpkg clean
make-kpkg --initrd --revision='2012.08.04-1' kernel_image kernel_headers modules_image

As described in the other guide. After booting the system, dmesg should give something like the following output, meaning the driver is loaded and detecting a harddrive:

Loading Adaptec I2O RAID: Version 2.4 Build 5go
Detecting Adaptec I2O RAID controllers...
Adaptec aacraid driver 1.1-5[2456]-ms
PCI: setting IRQ 11 as level-triggered
aacraid 0000:01:08.0: found PCI INT A -> IRQ 11
AAC0: kernel 4.1-0[7417]
AAC0: monitor 4.1-0[7417]
AAC0: bios 4.1-0[7417]
AAC0: serial 4EBB90
scsi0 : aacraid
scsi 0:1:0:0: Direct-Access   WDC   WD20EURS-63S48Y0 51.0 PQ: 0 ANSI: 2

The above steps are as stated required for an Adaptec 2610sa SATA controller. Slight changes should be required to make it work with any other SATA controller that is supported by Linux 2.6.27. In this example, I use a Western Digital 2TB drive (WD20EURS).
To see which low-level driver you have to install, check this page:

You might need these commands on the Raq to create the required devices:
mknod sda b 8 0
mknod sda1 b 8 1
mknod sda2 b 8 2
mknod sda3 b 8 3
mknod sda4 b 8 4
mknod sda5 b 8 5
mknod sda6 b 8 6
mknod sda7 b 8 7
mknod sda8 b 8 8
mknod sdb b 8 16
mknod sdb1 b 8 17
mknod sdb2 b 8 18
mknod sdb3 b 8 19
mknod sdb4 b 8 20
mknod sdb5 b 8 21
mknod sdb6 b 8 22
mknod sdb7 b 8 23
mknod sdb8 b 8 24

mknod sg0 c 21 0
mknod sg1 c 21 1
mknod sg2 c 21 2
mknod sg3 c 21 3

apt-get install lsscsi sg3-utils
lsscsi -vg
cat /proc/scsi/scsi
sg_map -i

To probe for PCI hardware:
apt-get install pciutils

This could give information like:
01:08.0 SATA controller: Initio Corporation INI-1623 PCI SATA-II Controller (rev 02)
which would mean to enable:
Initio 162x SATA support under "Serial ATA (prod) and Parallel ATA (experimental) drivers" in make menuconfig.

It is important to load a "noRAID" BIOS to your SATA card. This BIOS uses the SATA card like an IDE card which does not require any BIOS settings at startup, which can't be made on a Cobalt.

Further information:
admin / Dec 08, 2011
aacraid_guide.pdf: Adaptec AACRAID Linux User Guide
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