RDM vs VMFS


planning to run EV10 and E2K10 on ESXi, but now relalise more and more challenge…. one is how to support huge data (~30TB) for EV10.

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1004230
An ESX/ESXi host is limited to a maximum LUN size of 2047GB. This applies to all LUNs being presented to an ESX Server host (VMFS and RDM).

Use RDMs for Practical Reasons and Not Performance Reasons
http://vmetc.com/2009/04/13/use-rdms-for-practical-reasons-and-not-performance-reasons/

Use RDMs when VMFS virtual disk would become too large to effectively manage.
Use RDMs to leverage native SAN tools
Use RDMs for virtualized MSCS Clusters

Don’t use VMware Raw Device Mapping (RDM) for performance, but ..
http://www.virtualizationteam.com/virtualization-vmware/vmware-vi3-virtualization-vmware/dont-use-vmware-raw-device-mapping-rdm-for-performance-but.html

•No migrating VMs with physical mode RDMs if the migration involves copying the disk  (Storage VMotion)
•No VMotion with physical mode RDMs when any clustering software is used.
•No VMware snapshots with physical mode RDMs
•No VCB support with physical mode RDMs, because VCB requires VMware snapshots
•No cloning VMs that use physical mode RDMs
•No converting VMs that use physical mode RDMs into templates
VMFS vs RDM
http://funneverstops.net/?p=302

A few technical threads from the inside – Part 1: RDMs
http://virtualgeek.typepad.com/virtual_geek/2008/08/a-few-technical.html

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