Supported Platforms
Understanding Resilient Dual-Root Partitions on Switches
Resilient dual-root partitioning, introduced on Juniper Networks EX Series Ethernet Switches in Junos operating system (Junos OS) Release 10.4R3, provides additional resiliency to switches in the following ways:
- Allows the switch to boot transparently from the second root partition if the system fails to boot from the primary root partition.
- Provides separation of the root Junos OS file system from the /var file system. If corruption occurs in the /var file system (a higher probability than in the root file system due to the greater frequency in /var of reads and writes), the root file system is insulated from the corruption.
 | Note: For instructions on upgrading to release that supports resilient dual-root partitions from a release that does not, see the Release Notes. The procedure for upgrading to a resilient dual-root partition release is different from the normal upgrade procedure. |
This topic covers:
Resilient Dual-Root Partition Scheme (Junos OS Release 10.4R3 and Later)
EX Series switches that ship with Junos OS Release 10.4R3 or later are configured with a root partition scheme that is optimized for resiliency, as shown in Table 1.
Table 1: Resilient Dual-Root Partition Scheme
Slice 1 | Slice 2 | Slice 3 | Slice 4 | |
|---|---|---|---|---|
s1a | s2a | s3e | s3d | s4d |
/ (root Junos OS ) | / (root Junos OS ) | /var | /var/tmp | /config |
In the resilient dual-root partition scheme, the /var file system is contained in a separate slice from the root file systems, the /config directory is contained in its own slice, and switches ship from the factory with identical Junos OS images in slice 1 and slice 2. The /var file system, which has a greater frequency of reads and writes than the root file systems and is therefore more likely to have corruption issues, is isolated from the root directories and the /config directory. If the switch fails to boot, the system automatically boots from the alternate root partition. (If the switch fails to boot from the active root partition and instead boots from the alternate root partition, an alarm is triggered.)
Earlier Partition Scheme (Junos OS Release 10.4R2 and Earlier)
The earlier partition scheme is shown in Table 2.
Table 2: Earlier Partition Scheme
Slice 1 | Slice 2 | Slice 3 | |||
|---|---|---|---|---|---|
s1a | s1f | s2a | s2f | s3d | s3e |
/ (root Junos OS) | /var | (empty until initial software upgrade) | (empty until initial software upgrade) | /var/tmp | /config |
This is the partitioning scheme for a switch shipped with Release 10.4R2 or earlier (or after you reformat the disk during a downgrade from Release 10.4R3 or later to Release 10.4R2 or earlier). In this partitioning scheme, the switch comes from the factory with only one Junos OS image installed in the root Junos OS partition of slice 1. The first time that you perform a software upgrade, the new Junos OS image is installed in slice 2. If the switch fails to boot, you must manually trigger it to boot from the alternate partition (rebooting from the alternate partition does not occur automatically).
Understanding Upgrading or Downgrading Between Resilient Dual-Root Partition Releases and Earlier Releases
Upgrading from Release 10.4R2 or earlier to Release 10.4R3 or later differs from other upgrades in two important ways:
- You must install a new loader software package in addition to installing the new Junos OS image.
- Rebooting after the upgrade reformats the disk from three partitions to four partitions.
You can perform all operations for this special software upgrade from the CLI.
 | Caution: Back up any important log files because the /var/log files are not saved or restored during an upgrade from a nonresilient dual-root partition release to a release that supports resilient dual-root partitions. We recommend that you also save your /config files and any important log files to an external medium because if there is a power interruption during the upgrade process, they could be lost. |
