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Recovering the Primary Partition on EX4300-48MP Switches

 

This topic includes the following sections

Partitioning Scheme

The EX4300-48MP switch contains a single 50-Gigabyte SSD, which contains both the primary and backup partitions. The backup partition has a copy of the primary partition. The backup disk partition is used to recover the primary disk partition in the event that the primary partition gets corrupted. If the primary partition gets corrupted, a notification will be logged in syslog.

If the switch is booted from the backup partition, you can recover the primary disk partition by issuing the set system software add on-primary force-host command.

Note

Use the backup disk partition for recovery purposes only.

The EX4300-48MP switch SSD contains the following partitions:

  • /EFI

    This partition is approximately 200MB and contains GRUB (bootloader package) and BIOS capsules.

    If the primary EFI partition is corrupted, the system will switch to the backup EFI partition and boot the Host OS. Once the backup partition is active, the system will continue to work with the backup partition.

  • /boot

    This partition is approximately 1G and contains the files needed to boot the system.

    Files include the bzimage, initrd, GRUB, and the Junos OS configuration. The bzimage is the compressed kernel image, and initrd is the initial RAM disk. With initrd, a portion of the RAM is converted into the root file system, which is needed at system startup. When the kernel comes up, it might require a few drivers, and those drivers are loaded from initrd. After the system comes up, initrd is unmounted.

    If the system boots up from backup partition, the system will continue to work from backup /boot partition.

  • /root

    This partition is approximately 2G and contains all directories and subdirectories. If the system boots up from the backup partition, the system will continue to work from the backup /root partition.

  • /var

    This partition contains the user home directory, log files, and temporary storage and is backed up completely.

    This partition is available on the backup partition if the system boots up from backup partition.

  • /junos

    This partition contains both the primary and backup Junos qcow disk images.

    The qcow (qemu copy on write) is the file format used by qemu VMM (virtual machine monitor), which optimizes the storage allocations.

    The images are contained in the /images/0 (primary) and /junos/images/1 (backup) directories. When the switch is booted from the backup partition, Junos OS boots with the image from /image/0. If /image/0 fails to boot up, the backup image from /image/1 is booted.