Quartz 4

Recent Notes

Disk

3 min read

Disk partitioning is dividing a hard drive into multiple logical storage units.

Partitioning schemes: How to partition disk, how many partitions can be, sizes, locations etc. are determined by partition schemes (GPT & MBR)

mount -a : mount everything in /etc/fstab file (without the ones with noauto)

MBR

An old technology (1982). Compatible with old hardware and software.

  • Uses BIOS

  • Supports maximum 4 primary partitions. You can create 3 primary and 1 extended partition and with logical partitioning, you can create a maximum of 15 partitions.

  • Disk partitions are limited to 2TB.

  • Uses 32 bits for storing logical block addresses and size information.

Note: An OS can not be installed on logical drive.

  • First few sectors of a disk is always reserved. It is for OS to understand that where it will write data on disk.

  1. Sector: MBR (512 bytes)

    1. Boot sector (446 bytes)
    2. Partition sector (64 bytes)
    3. Magic number, The magic number serves as a validation check of the MBR. If it is a valid MBR, value is AA55. If value is different, disk is corrupt. (2 byte)

  2. Sector: LVM (512 bytes)

  3. Sector: LVM Metadata (512 bytes)

  4. Sector: Metadata backup (512 bytes)

GPT

Stands for “GUID Partition Table”. A newer technology. Address many of the limitations that the old MBR-based scheme imposes.

  • Uses UEFI. GPT is a part of UEFI standard.
  • Support maximum 128 partitions
  • Allocates 64 bits for logical block addresses. This allows a GPT to accommodate partitions and disks size up to eight zebibytes (ZiB).
  • Uses a GUID (globally unique identifier) to identify each disk and partition.
  • In contrast to MBR, which has a single point of failure, GPT offers redundancy of its partition table information.
  • GPT uses a checksum to detect errors and corruptions in the GPT header and partition table.

Note: In MBR, if MBR sector in the head of the disk corrupt, there is no way to recover. But in GPT, primary GPT resides at the head of the disk, while a backup copy, the secondary GPT, is housed at the end of the disk.

udevadm: The udevadm command ****is a device management tool in Linux which manages all the device events and controls the udevd daemon.

udevadm settle: After partitioning, this command tells kernel to update itself for hardware changes using udevd daemon

Storage Protocols & Interfaces

InterfaceProtocolLinux DeviceSCSI-based?Use Case
SATASATA/dev/sdXIndirectlyConsumer HDD/SSD
SASSCSI/dev/sdXYesEnterprise storage
NVMeNVMe/dev/nvmeXnYNoHigh-performance SSDs
iSCSISCSI/IP/dev/sdXYesNetwork block storage
USBUSB/UAS/dev/sdXIndirectlyExternal drives

Graph View