2.1 Design Hard Disk Layout

22Jan - by qkim0x01 - 0 - In Private Notes

This is a note I made while I was reading a book about Linux

@: Command, +: File, #: Example

System Considerations
- – amount of disk space
- – size of the system
- – use of system
- – how and where to backup

Limited disk space
- – Depends on system requirement and available filesystem resource

Mount point
- – before go into filesystem, I need to list them in a filesystem table
  - – Mounting
    - – the process of listing filesystem
  - – The directory I’m mouting on
- + /etc/fstab
  - – mount point is managed by this on system start up

Superblock
- – a block on each filesystem contains metadata
  - – about filesystem layout
  - – type, size, status of filesystem
- – equivalaent to File Allocation Table (FAT)
- – keep redundant copies of superblock

MBR
- – Master Boot Record (MBR)
- – contains information about hard disk partitions
- – loads OS
- – located in first sector of hard disk
  - – 512 bytes
- @ dd
  - – to back up MBR
  - # dd if=/dev/hda of=/~/mbr.txt count=1 bs=512
    - – assuming hard drive is /dev/hda
    - – one copy (count=1)
  - # dd if=~/mbr.txt of=/dev/hda count=1 bs=512
    - – to restore

Booting from a USb device
- – Live usb or Live CD
  - – can write back to USB, but not CD
- – need to make the USB bootable
  - – set at least one partiions of USB with the bootable flag to primary partition
  - – MBR mush write to the primary partition
- – need BIOS setting to boot USB

Backup
- – some schemes use disk partitions as the basic unit
  - – filesystems in /etc/fstab is backed up separately
  - – they are arranged so each filesystem fits within the size of backup media
- @ dd
  - – back up each partition
  - # dd if=/dev/hdx of=/dev/hdy
- @ sfdisk
  - – create a copy of partition table
  - – back up of the partition layout
  - # sfdisk -d /dev/hda > parition_backup.txt
  - # sfdisk /dev/hda < partition_backup.txt
- @ df
  - – report file system disk space usage

Swap space
- – or virtual memory
- – to temporarily store portions of main memory that are not needed now
- – old rule
  - – double of RAM

General Guidlines
- – keep (/) simple
- – seperate a small /boot partition below cylinder 1024
  - – for installed kernels used by boot loader
  - – not for newer BIOS and kernels (eg., 2.6.20)
- – Separate /var
  - – big enough for logs, spools, mail
- – separate /tmp
  - – depends on demands of applications
- – separate /usr
  - – make it stand alone
- – separate /home
  - – for multiple users
  - – put /home on a disk array and use Logical Volume manager (LVM)
- – set swap as at least of RAM

qkim0x01

Operating Systems