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    Best Practices for Boot Mode Legacy BIOS and UEFI

    Last updated: 2024-01-06 17:43:10
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      The boot mode refers to the method of booting the system disk when a CVM instance is created, the description of which can be found in the image parameters .
      CVM supports two boot modes: Legacy Basic Input/Output System (Legacy BIOS) and Unified Extensible Firmware Interface (UEFI). The differences between these two modes, and the specific boot modes supported by CVM instances will be introduced in this document.

      Differences Between Legacy BIOS and UEFI Boot Modes

      Comparison Item
      UEFI Boot Mode
      Legacy BIOS Boot Mode
      System Boot Process
      UEFI utilizes GPT (GUID Partition Table) as its partition scheme and supports hard disks larger than 2TB and multiple partitions.
      Legacy BIOS employs the MBR (Master Boot Record) as its partition scheme, supporting hard disks up to 2TB and a maximum of four primary partitions.
      Boot Speed
      UEFI provides a faster booting speed as it can directly interact with the operating system.
      Legacy BIOS has to load the operating system via a boot loader.
      Secure Boot
      UEFI offers the Secure Boot feature, which can prevent unauthorized operating systems and boot loaders from booting.
      Legacy BIOS does not have a Secure Boot feature like UEFI.
      User Interface and Operations
      UEFI provides a graphical interface and a wider range of operation options.
      Legacy BIOS typically provides a basic text-mode interface.
      Compatibility
      UEFI is a relatively new technology, supporting more hardwares and operating systems.
      Legacy BIOS is a relatively old technology that may encounter compatibility issues on certain new hardwares and operating systems.
      Firmware Size
      UEFI firmware is typically larger in size than Legacy BIOS firmware due to its incorporation of more features and drivers.
      Legacy BIOS firmware is typically smaller in size than UEFI firmware.
      System Diagnostics and Recovery
      UEFI boot mode generally offers a more comprehensive set of system diagnostic and recovery tools, aiding in an easier system repair and recovery process when issues arise.
      Compared to UEFI, Legacy BIOS has a less extensive set of system diagnostic and recovery tools.
      In summary, UEFI and BIOS are two different boot modes, differing in the boot method, speed, security, interface, compatibility, and firmware size. When selecting a boot mode for your server image, you should carry out an assessment based on your hardware and operating system requirements.
      Note:
      For the performance of an instance, there is typically no significant differences between different boot modes. The boot mode primarily influences system start-up procedures, disk partition schemes, and boot loaders, but not directly affect the performance of an instance when it is running.

      Public Image Boot Mode Description

      1. Public images with the UEFI version suffix use UEFI boot mode (such as TS 3.1 (TK4) UEFI version); those without the UEFI version suffix use Legacy BIOS boot mode.
      2. For all the public images of ARM version, UEFI boot mode is used.
      You can also click image ID on the CVM console - Image page to view details.

      Custom Image Boot Mode Description

      1. Importing Custom Image: You can configure the boot mode of the image.
      Please confirm that the selected boot mode aligns with the boot mode of the image file. Otherwise, using this image could affect the normal boot of your instance.
      2. Creating Custom Image: It will inherit the boot mode of the image currently used by your instance.
      You can also click image ID on the CVM console - Image page to view details.

      Boot Mode Description Supported by Instance Type

      Note:
      When a CVM is purchased, the system will automatically identiy the image boot mode available to the instance type. Images with incompatible boot modes cannot be selected.
      The table below provides references for understanding the compatibility of boot modes with different types of instances:
      Boot Mode
      Instance Type
      Only supports Legacy BIOS
      CVM_x86 models: Old-generation models such as Standard S1/S2/S2ne, Memory Optimized M1/M2, High IO I1/I2, Compute Optimized C2/CN2, and Big Data D1, and so on.
      Bare Metal: All bare metal models support only Legacy BIOS.
      HCC: Standard HCCS5, HCCIC5, HCCPNV4h, HCCG5vm, and HCCG5v.
      Only supports UEFI
      HCC: GPU model HCCPNV5.
      ARM Models: Only UEFI boot mode is supported.
      Compatible with both Legacy BIOS and UEFI
      CVM_x86 Models: Except some old-generation models that only support the Legacy BIOS boot mode, the other new generation CVM_x86 models are compatible with these two boot modes.
      Heterogeneous GPU Models: Compatible with these two boot modes.
      
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