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As cache size has grown, the time required to move all cached data to a persistent state has also increased. Vaulting is designed to limit the time needed to power off the system if it needs to switch to a battery supply. Upon complete system power loss or transitioning a system to an offline state, PowerMaxOS performs a vault of cache memory to dedicated I/O modules known as flash I/O modules. The flash I/O modules use NVMe technology to safely store data in cache during the vaulting sequence.
Lithium-ion standby power supply (Li-ion SPS) modules provide battery backup functionality during the vault operation. Two SPS modules are configured per engine. The SPS modules also provide back-up power to the InfiniBand switches in applicable configurations.
State changes that require the system to vault are referred to as vault triggers. There are two types of vault triggers: internal availability triggers and external availability triggers.
Internal availability triggers are initiated when global memory data becomes compromised due to component unavailability. Once these components become unavailable, the system triggers the Need to Vault (NTV) state, and vaulting occurs. There are three internal triggers:
Vault flash availability: The NVMe flash I/O modules are used for storage of metadata under normal conditions, and for storing any data that is being saved during the vaulting process. PowerMax systems can withstand failure and replacement of flash I/O modules without impact to processing. However, if the overall available flash space in the system is reduced to the minimum to be able to store the required copies of global memory, the NTV process triggers. This is to ensure that all data is saved before a potential further loss of vault flash space occurs.
Global memory (GM) availability: When any of the mirrored director pairs are both unhealthy either logically or environmentally, NTV triggers because of GM unavailability.
Fabric availability: When both the fabric switches are environmentally unhealthy, NTV triggers because of fabric unavailability.
External availability triggers are initiated under circumstances when global memory data is not compromised, but it is determined that the system preservation is improved by vaulting. There are three external triggers:
Input power: If power is lost to both power zones, the system vaults.
Engine trigger: If an entire engine fails, the system vaults.
DAE trigger: If the system has lost access to the whole DAE or DAEs, including dual-initiator failure, and loss of access causes configured RAID members to become non-accessible, the system vaults.