Release Notes

Data Drives
17 Best Practices for Implementing VMware vSphere in a Dell PS Series Storage Environment | TR1091 | v1.3
6.3 Raw Device Mapped LUNs
Raw Device Mapped LUNs (RDMs) are used to isolate the data on volumes and retain the view inside
vCenter.
Advantages:
• Easy to configure: Each RDM is a single volume on the SAN
• Viewable in vCenter under the VMs to which it is attached: The volume is displayed inside vCenter
under the VM and enables vCenter integration with software such as SRM
• Enables tiering of data drives to different volumes or pools based on workload: It is possible to isolate
the data drive RDMs to another tier of storage for performance
• Uses vSphere MPIO for high bandwidth Apps: Continues to leverage the MEM or Round Robin for
multipathing
• Isolates data from OS and enables the use of 3rd party applications which work with RDMs: There
are some 3rd party applications that require some form of RDM for either backup or protection or
tools
Disadvantages:
• No guest integration with Auto Snapshot Manager/Microsoft
®
Edition: ASM/ME cannot recognize
RDM volumes for Smart Copy operations
• No VM integration with VSM Smart Copies: VSM does not recognize RDM volumes for Smart Copy
operations for VM snapshots
• Each ESXi server needs connectivity; connection counts need to be evaluated: Since each ESXi
server needs to see the RDM volume, there are multiple connections to the RDM even though only
one server is using the volume at a time.
Configure RDMs with the same best practices as VMDK on VMFS with the new SCSI adapter and
paravirtualized adapter if supported.
6.3.1 VM data drive formatting options
Dell EMC has found improvements in performance by using a 64k partition alignment. This is necessary in
Windows Operating Systems before Windows 2008, Oracle
®
Solaris, and Red Hat
®
Enterprise Linux
®
guest
OSs. Additionally, Microsoft
®
SQL, Exchange
®
, and other I/O intensive applications benefit from formatting the
filesystem with a 64K cluster size. This format achieves a better alignment of I/Os with the 64K stripe size of
the PS Series arrays.