HP manual Using Windows page files with the IO Accelerator, Introduction to Windows page files

Using Windows page files with the IO Accelerator

Introduction to Windows page files

This section describes how to effectively use paging (swap) files on IO Accelerator devices with Windows® operating systems.

Using a page file with a traditional disk drive places practical limits on the usable size of the page file and virtual memory due to the poor performance of disk drives in relation to RAM. Placing the operating system paging file on one or more IO Accelerators enables much larger page files and usable virtual memory. This is due to the much faster response times and bandwidth on IO Accelerators versus hard disks. IO Accelerator software prior to version 2.0.2 does not support paging files.

Configuring IO Accelerator paging support

The IO Accelerator 2.0.2 driver and later versions can be configured to support paging files on one or more IO Accelerators. Configuring paging support requires that each IO Accelerator used with a paging file preallocates the worst-case amount of memory it might need in any possible I/O scenario. Memory is pre-allocated on a per-adapter (ioDIMM) instance.

Because of the extra host RAM memory use, paging must be enabled only on IO Accelerators that actually hold a paging file. You can place a single paging file on more than one IO Accelerator. Windows® operating systems stripe paging I/O across all available paging files, providing additional performance to the VM subsystem.

RAM consumption

The amount of RAM preallocated per IO Accelerator depends on the total size of the device and the sector (block) size selected when formatting the drive (with fio-format). The following table lists the estimated memory consumption for the various device and sector sizes.

IO Accelerator size (GB)	512 byte sector	4096 byte sector
80	2,278	284
160	4,556	569
320	9,132	1,141
640	18,264	2,282

Host RAM Consumption in Mebibytes (MiB); 1024 x 1024 = 1 MiB

Using a larger sector size significantly reduces the amount of host memory consumption needed for paging support. HP recommends using a 4K sector size be used because:

•that is generally the natural size of a host memory page, and

•it minimizes overall host memory consumption.

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