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The Apache Pass memory, i.e. each of the systems, can be configured in two (three) modes:
- Memory Mode: The Apache Pass/Optane Memory is exposed as RAM to the OS. Although the hardware technology is different to DRAM, this mode allows transparent usage of the SCM memory. The main benefits are the gained memory capacity and easy usage (no modification of applications required). The DRAM memory acts as cache for Optane Memory. In this mode, the SCM is effectively not persistent.
- AppDirect Mode: The Apache Pass/Optane Memory is exposed as block device(s) to the OS (usually as /dev/pmemX, depending on actual configuration). On such block devices, a file system can be created which should support the direct access (DAX) option. This allows to map data on the persistent Optane Memory into an application's virtual address space while avoiding the OS' page cache. Thus, direct media access to the SCM is possible with load/store operations. Note that data on the Optane Memory is effectively cleared when the mode is changed. Therefore, data on /dev/pmemX should be considered as ephemeral.
- (Mixed/Hybrid Mode: The System can also be configured to provide a portion of the Optane capacity for the Memory Mode and another portion for AppDirect mode.)
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