Limitations of RDM LUNs managed by SnapDrive

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SnapDrive has a few limitations for provisioning RDM LUNs. You must be aware of the limitations that might affect your environment.

  • An RDM LUN cannot serve either as a boot disk or system disk.

  • SnapDrive does not support MPIO in the guest operating system, although VMware ESX server supports MPIO.

  • When the transport protocol is FC, the igroup that is specified in the CLI command is ignored by SnapDrive, and the igroup is automatically created by the virtual interface.

  • You can rename, move, or delete the /usr/bin/rescan-scsi-bus.sh script that is bundled as part of sg3_utils to avoid limiting the number of RDM LUNs to eight.

    Note If you want to retain /usr/bin/rescan-scsi-bus.sh in sg3_utils and avoid limiting the number of RDM LUNs to eight, then you must create a wrapper script /root/dynamic-lun-rescan.sh and from that script run /usr/bin/rescan-scsi-bus.sh, with the options -w, -c, and -r and assign full permissions.

The following is an example of the modified content of /root/dynamic-lun-rescan.sh:

#cat /root/dynamic-lun-rescan.sh
#Wrapper script used to call the actual rescan script.
/usr/bin/rescan-scsi-bus.sh -w -c -r

Limitations related to VMware ESX server

  • Each guest operating system can be configured with four SCSI controllers, and each SCSI controller can be mapped to 16 devices.

    However, one device is reserved per controller, and therefore a total of 60 (16 *4 — 4) RDM LUNs can be mapped to the guest operating system.

  • Each ESX server can be mapped to a maximum of 256 RDM LUNs.

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