Home > Storage > PowerMax and VMAX > Storage Admin > Reliability, Availability, and Serviceability on PowerMax 2500 and 8500 Arrays > Persistent Memory (PMEM)
PowerMax 2500 and 8500 Arrays use a type of memory known as persistent memory which combines the durability of flash storage while approaching the performance of more expensive DRAM. Instead of using electrons to store information, it uses heat to change the cell's state, from amorphous to crystalline, changing its resistance. By doing this, the PMEM can retain its data even after the power is off.
PMEM comes in the form of AEP (Apache Pass) DIMMs (Dual In-Line Memory Modules) which are used to store persistent metadata in Apache Pass (3DXPoint NVDIMM Memory). This is achieved using an Intel proprietary modification to the DDR4 spec and this gives 10’s of nanoseconds access time.
PMEM is used to store system metadata, which comes in various forms such as data structures, pointers, scatter gather lists, and so on. Efficient metadata processing requires that the CPU has quick access to the metadata, meaning that it needs to be accessible in memory within the system. The use of PMEM to store metadata improves system efficiency as the systems scale out.
With PMEM, more efficient data vaulting is achieved, because the data is persistent and does not require vaulting during shutdowns or other vault trigger scenarios. This results in lower system demands when moving data to the self-encrypting NVMe vault drives. This improves vaulting speed and lowers the keep alive time requirements for the internal battery backup mechanism.