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Dell PowerFlex 4.5.x Technical Overview

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Configure direct attached storage

When adding direct attached storage to SDS, it is recommended to configure the raw devices as stand-alone devices. Upon adding a device to an SDS PowerFlex verifies that the device is clear and returns an error if it is otherwise.

PowerFlex works with any free capacity—internal or direct-attached devices, either magnetic hard disk drives or flash-based devices such as solid state drive (SSD) and PCIe cards. Although PowerFlex can work with any device topology, it is recommended to configure the raw devices as stand-alone devices.

Device data is erased when devices are added to SDS. When adding a device to an SDS, PowerFlex checks that the device is clear before adding it. An error is returned, per device, if it is found not to be clear. You can override this check by using the force device takeover option.

The following devices are considered to be not "clear," and thus cannot be added to SDS:

  • Linux - A complete device with either a file system or partition, or a partitioned device with a file system.
    • Multipath devices cannot be added as SDS devices.
    • Devices in an LVM group cannot be added to an SDS.
  • ESXi - Same as above, depending on the operating system of the SVM where the SDS is installed.

Limitations:

  • SAN devices will not be prevented from being added.
  • Devices in an LVM group cannot be added to an SDS.
  • Within the database devices, only Oracle ASM devices can be detected and blocked.
NOTE:

If the server has a RAID controller, PowerFlex prefers to use the caching abilities of the controller for better performance, but is better used when all devices are configured as stand-alone (that is setting each of the devices to RAID 0 separately). Dell Technologies recommends enabling RAID controller caching for hard disk drive devices. Caching is not needed for SSD devices.

NOTE:

For hard disk drives: It is recommended to use RAID controller caching when available as follows:

  • READ/WRITE: If the cache is battery-backed
  • READ ONLY: If the cache is NOT battery-backed

For SSDs (such as Flash): setting should be write-through

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