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What is Intel Optane Persistent Memory Dual Mode?


Intel Optane persistent memory has two modes of operation: memory mode (memory model) and APP Direct mode, regardless of which mode you can always use available large capacity memory. speed of machine is faster, speed of various programs can only be faster, not slower, and upgrade of system will also become faster.

As mentioned in previous article, as charge improves, latency will not increase like NAND. Optane has such a feature that it does not need to be erased before writing, but can be written directly.

What is Intel Optane Persistent Memory Dual Mode?

Intel Optane DC Persistent Memory

Internal mode: high capacity, available, volatile

When configured in memory mode, applications and operating systems see it as a pool of volatile memory, no different from today's DRAM-based systems. In this mode, no application program is required to program ROM and data is lost when power is turned off.

In memory mode, DRAM is used as a cache for high frequency hot data, but capacity of Intel Optane data center persistent memory can be very large, and memory controller of Intel Xeon Scalable processor manages cache.

When memory needs to read data, memory controller first checks DRAM cache if there is one, then reads data from DRAM, latency is very low. If there is no such data in DRAM, data is read from permanent memory of Intel Optane data center, and latency will be correspondingly higher.

When number of applications is relatively stable, matching with memory controller can improve cache hit rate, and naturally performance will improve accordingly, similar to DRAM. When randomness of requested data is relatively large, performance will be worse, at around 100 nanoseconds.

In memory mode, data is volatile and will be lost when power is turned off. Lossless mode is second mode, called App Dircet mode.

Memory mode provides high capacity and low cost memory for native applications, including virtualized databases, which is very suitable for big data analytics applications.

App Direct Mode: Large Memory, Affordable Price, Non-Volatile Memory

App Direc has not yet seen an official translation. It might be more appropriate to change App Direct to "app direct connection" mode. The data acquisition process was relatively convoluted. App Direct In this mode, an application can be directly connected to hardware, obtain storage via a DDR memory channel, and use file system as memory, without software having to do so. too many fixtures and modifications.

When configured as App Diect, application and operating system will recognize that there are two direct load/save memory modes and will automatically determine which reads and writes are appropriate for DRAM or Optane non-volatile memory.

Data that requires low latency and does not require long-term storage can be placed in DRAM. Large amounts of data that require persistent storage or structured storage are suitable for placement in Optane datacenter's persistent storage. If you want data to be stored in memory, you must select App Direct mode.

In-memory databases and in-memory analysis platforms are very suitable for applications that require faststorage. Optane persistent memory has its own characteristics, but there are still applications for which it is very well suited.

App Direct mode must be able to identify persistent memory filesystem, which requires operating system or virtual environment support, including Microsoft Win Server 2019, Ubuntu, Red Hat, VMware ESX v6.7, all support Optane datacenter memory persistence , Cisco Hyperflex hyperconvergence and RDMA technology are also supported.

The mode determines how much memory system can use. In App Direct mode, non-volatile DRAM and Intel Optane DC. In memory mode, both DRAM and Optane non-volatile memory are considered memory. In memory mode, DRAM is used as cache and does not appear as a separate memory resource. In other words, system does not recognize it as memory.

For example, platform has 1,536B of Intel Optane persistent memory and 192GB of DRAM. If it is in App Direct mode, system will display 1,728 TB of memory. If it is in memory mode, it will only show 1.536 TB of memory.

The system administrator can configure this mode using BIOS or internal management tools, and can also partition memory pool into sections, and different partitions can work in two modes at same time.

Memory data can be leaked in App Direct non-volatile mode. A more secure way to clear memory is to lose memory encryption key, but it doesn't work in a shared memory scenario, which is more reasonable. path This refers to TRIM command used in SSD.