SDB:An Advanced Discussion on Partitioning a BOOT or Root Partition of a Hard Disk

From openSUSE

Version: 10 - Perpetual Relevance from V10

Purpose

The Purpose of this document is to discuss the issues and problems that may arise when physically partitioning multiple IDE and SATA drives in combination, using the openSuse Partitioner on an I386 PC. This procedure is largely dependant on the chipset, BIOS, architecture and the disk controller being part a physical IDE/SATA device. This discussion is of little value in SCSI device arrays or Hardware RAID devices.

Scope

The scope of this document may be further limited to, or incorrect, dependant on the chipset of your motherboard and BIOS. If a Hardware RAID device is connected to your motherboard this too is outside the scope of this document.

Audience

The audience of this document is aimed at those accustomed to using or starting to use the openSuse Expert Partitioner with a degree of confidence and those wishing to expand on their current knowledge.

Discussion

The Primary Drive containes the MBR and boot sequence and Operating System other drives if present may contain data or any other mount point in the directory structure. Every PC has a Primary drive which must contain the Master Boot Record with or without a direct association of the O/S. Custom Partitioning can easily create a situation where the MBR is written to one device along with the Boot or Root Partition. The data, or any other mount point can reside on a different device and indeed this is not unusual, however many considerations are required in any customise partitioning and format.

The advent of the IDE type drive was an alternate to that of a SCSI drive array. It differed primarily from the SCSI drive array in that the IDE drive contained within the drive the Disk controller. If your primary goal is to setup and partition a File Server there is a very good reason to choose SCSI HDD rather than multiple IDE/SATA devices.

SCSI devices are far more likely to provide more acceptable Disk read/write times in a situation where the demands of your File Server are considerable. Multiple IDE/SATA devices will NOT provide the demands of redundancy, data security and possible data loss of a failed controller within an IDE/SATA device. Exercise extreme caution in creating ANY RAID partition using a Reiser format as you may never be able to delete the partition. An expert, non native OpenSuse partitioner is needed to ever delete a RAID Reiser formatted partition.

Another tip is to use a mirrored 2 x IDE devices for the boot (MBR) or root partition and O/S. It becomes far easier to load SCSI drivers, if required, after your O/S has already been installed and running and partition and mount data points as needed on the SCSI array.

It is the personal Opinion of the author that Hardware RAIDS based on either an IDE or SATA, never be installed.You can easily establish you MBR as in the tip above and install SCSI cards, which provides for a huge number of physical drives. I find little value in IDE Hardware RAID cards - especially if you require real performance and the flexibility that SCSI is innately designed for achieving.

Today's motherboards normally, but not limited to, support 2 x IDE channels and 2 x SATA channels. For each channel physically can contain, 2 x IDE devices and 2 channels containing 2 SATA devices. The Primary drive on each channel is hardware selected to be either Master or Slave and sometimes hardware selected to permit the positioning of the device on the cable to dictate its function. I.E The end of an IDE cable when a device is so installed will assume the role of Master by virtue of its positioning. The hardware selection of the Primary Master device will either overrule or conflict any BIOS conditions that specify any device in its device priority list in or separately in the Boot Order. In situations where the BIOS records an IDE as Primary Master and a SATA device as Secondary Master, my well require that the MBR or boot or root partition be created on the SATA device. This is often the case.

Consider a motherboard that has 4 IDE devices,defined in BIOS as; a Primary Master, a Primary Slave, a Secondary Master and Secondary slave. Here the boot sector partitioning MUST be located on the Primary Masters Drive otherwise the system will NOT boot even in a situation where a secondary drive has been partitioned and formatted as the boot or root of the O/S and listed in BIOS as the boot device. The question here is which drive does the O/S consider to be the Primary drive. The result is not always clear and is fundamentally elected by the motherboards BUS. As always the OpenSuse install program will select the device which must carry the MBR. If you want to use custom partitioning it is wise to retain the device install selects as the boot or root device.

Enter the next complication where the same configuration has been extended to also contain a Primary Master SATA device, a Primary Secondary SATA device, a Secondary Master IDE device and a Secondary Slave IDE device.Traditionally, but not always, the Primary SATA device normally will be the root or boot device, but yet again pay attention to the device select by install and custom partition, if required, but keep the device auto selected by install as the boot or root device.

Now we have many 'Master' devices. The question is which drive IS now the Master Device. The answer will NOT be in the system BIOS nor will the hardware be overruled by BIOS priority settings and almost certainly not be overruled by editing the Boot Loader. Editing the Boot Loader to set the Primary Master Device, contrary to the system selected Primary Master Device, which has been determined by the Hardware BUS. In this situation changing the Boot Loader may or may not dictate the Primary Master Device.

Reliably Selecting the Boot or Root Device

Before you start to load up your PC with multiple devices check your motherboard specs as some hardware can not deal with 2 x 2 IDE devices and 2 x 1 SATA devices. In some cases if you have 2 x 1 SATA devices, 1 IDE device must be vacated and vicar versa.

Many of us have performed custom partitioning of our drives and despite nominating what we consider to be the Primary Device as either the boot or root partition the system will fail to boot the O/S from the Hard Disk.

By far the easiest way to determine the Primary Master Device is to note carefully which device the install program selects for the boot or root partition PRIOR to using any custom partitioning. Once the install system has selected the root or boot device you can enter the custom partitioner with safety as long as you maintain the same device as the boot or root device that was selected by the install program. One word of caution – if you intend to set-up the boot or root device partition on the Primary Master Boot device and mirror it (RAID 1) you may get into a lot of trouble by selecting the redundancy mirror on the other Primary Master Device that was NOT selected by install as the boot device. In other words if install selects the boot or root device as being the Primary Master SATA device exercise caution in mirroring this partition on the Primary Master IDE device. Depending on your systems motherboard chipset and BIOS this may determine if you will be successful or not in such an example.

Because of the Master/Slave relationship of 2 devices under IDE, the physical failure of 1 device controller will often effect the other device on the same connection cable. The is no value in selecting any redundancy RAID on a device on the same connection cable. Redundancy disk capabilities should only be considered on either a device on a different connection cable or a SCSI array or Hardware RAID.

Another word of caution is related to a PC which has an excess of 4 Hard Drives. The more IDE/SATA drives you have in each PC the hotter they will run. This is due to the overhead of each device controller within each device synchronising with subservient or dependant devices.

Most devices are S.M.A.R.T enabled and the temperature overhead of each drive will be evident in the System Log which can be viewed dynamically using KsystemLog in the openSuse Software as an options and is not loaded by default. The more devices the higher the controller overhead and the hotter the devices will run and frequently require dedicated air displacement services within the PC to avoid miss reads / writes / verifies and corruption of sectors.

SATA devices traditionally run much hotter than IDE devices. Alarms should start to ring loudly if the temperature of an IDE device rises above 90 degrees Celsius and a SATA device runs above 100 degrees Celsius as reported by SMART monitoring as attribute 194. Again you will need view KsystemLog dynamically and make sure that the SMART process is running and the drives are SMART compatible. The process is defined in the system log as 'smartd'

Notes

For those who wish to set-up a dedicated File Server of any description the Installation of 2 x SATA Devices followed by a SCSI array offers the following benefits. The MBR Record or Boot drive can easily be set up on Mirrored SATA devices and the Data be set-up on the SCSI disks. By using this philosophy you will never run into a situation where you need to load thrid part disk drivers for the SCSI drives,before you commence with the Installation.

If problems ever arise with the software Disk Driver of a SCSI drive, and the SCSI drive contains the MBR and instructions, you may never be able to get easy and uncomplicated access to the MBR and instructions. By Mirroring a Redundancy on 2 x SATA drives containing the MBR and other start-up files the volume that the SCSI drives contains is easily accessible as no third part or drive specific drivers are required. The Data Volume can then be ever increased by adding more SCSI drives without ever altering the MBR and Start-up file on the SATA drives which contain no software drives to view or mount.

Links

This is NOT the Perfect example the author could find however, it graphically illustrates the install and customisation of the Hard Disk. More needs to be written in the SDB on customisation of multiple disks and partitions with OpenSuse Expert Partitioner. http://www.howtoforge.com/perfect_server_opensuse10.3

en:SDB:Partitioning_Boot_Sector_with_Multiple_IDE/SATA_devices