Nvs Cards - Juniper ERX - RELEASE 11.1.X HARDWARE GUIDE 03-23-2010 Hardware Manual

Chapter 1: ERX Overview
ERX7xx and ERX14xx models use a 1:1 redundancy scheme for the SRP module.
When two SRP modules of the same type are installed in the chassis, one acts as a
primary (active) and the second as a redundant (standby) module. Both SRP modules
share a single SRP I/O module located in the rear of the chassis.
If the standby SRP module detects that the primary SRP module is not active (and
high-availability mode is not enabled), it reboots the system and takes control. If
high-availability mode has been enabled, automatic switchover occurs with near
hitless failover. If you upgrade software, you must copy the software to the redundant
SRP and reboot it. For information about configuring and managing SRP module
redundancy, see JUNOSe System Basics Configuration Guide, Chapter 6, Managing
Modules.
After you install two SRP modules, the modules negotiate for the primary role. A
number of factors determine which module becomes the primary; however,
preference is given to the module in the lower-numbered slot. The SRP modules
record their latest roles and retain them the next time you switch on the system. For
information about installing SRP modules, see "Installing Modules" on page 31.

NVS Cards

If you have two SRP modules installed in a system, you can use NVS cards of different
capacities on the SRP modules. The effective capacity of the higher-capacity NVS
card will equal that of the lower-capacity NVS card. For information about installing
NVS cards, see "Installing Modules" on page 31.
When you install new NVS cards or SRP modules, you must issue the synchronize
command to match the file system of the NVS card on the redundant SRP module
with the file system of the NVS card on the primary SRP module. (The NVS card on
the redundant SRP module will hereafter be referred to as the redundant NVS card;
the NVS card on the primary SRP module will hereafter be referred to as the primary
NVS card.)
If the capacity of the primary NVS card is equal to or smaller than that of the
redundant NVS card, the system copies all the files from the primary NVS card to
the redundant NVS card. However, if the capacity of the primary NVS card exceeds
that of the redundant NVS card, the system creates an invisible synchronization
reserve file on the primary NVS card, provided that there is enough space for the
file.
The purpose of the synchronization file is to prevent the creation of data that cannot
fit on the redundant NVS card. The file contains no useful data, and is not visible
when you view the files in NVS. The size of the file is equal to the difference in
capacities of the two NVS cards. For example, if the primary NVS card has a capacity
of 224 MB and the redundant NVS card has a capacity of 220 MB, the size of the
synchronization file is 4 MB, and only 220 MB of space is available on the primary
NVS card.
If the primary NVS card does not have enough space to create the synchronization
reserve file, the synchronize command fails, and a warning message is displayed
on the console. To resolve this issue, either delete unwanted files from the primary
NVS card or replace the redundant NVS card with a higher-capacity NVS card.
15
Redundancy Features