27 Oct 2009 @ 8:34 AM 

I was looking at my Google Analytics account and realized i am getting alot of hits for the keywords “ESX 4.0 RDM greyed out” which i briefly questioned in a previous post. The answer to this is simple, to be a `supported` Raw Device Mapping (RDM!) you need an available and unformatted LUN (SCSI, iSCSI, Fibre Channel etc.) to map to a .vmdk file.

As i pointed out in a previous post, it is rather easy to create an RDM manually via command line:

esxcfg-scsidevs -l

Output:

t10.ATA_____SAMSUNG_HD502HI_________________________S1VZJDWS462094______
 Device Type: Direct-Access
 Size: 476940 MB
 Display Name: Local ATA Disk (t10.ATA_____SAMSUNG_HD502HI_________________________S1VZJDWS462094______)
 Plugin: NMP
 Console Device: /dev/sda
 Devfs Path: /vmfs/devices/disks/t10.ATA_____SAMSUNG_HD502HI_________________________S1VZJDWS462094______
 Vendor: ATA       Model: SAMSUNG HD502HI   Revis: 1AG0
 SCSI Level: 5  Is Pseudo: false Status: on
 Is RDM Capable: false Is Removable: false
 Is Local: true
 Other Names:
 vml.01000000005331565a4a44575334363230393420202020202053414d53554e

The above output was truncated to focus on the disk I am creating a RDM for, but that command will list ever disk and its detailed information; and is new to ESX 4.0. So now that I have my drive identifiers, I can create an RDM like this:

vmkfstools -r /vmfs/devices/disks/t10.ATA_____SAMSUNG_HD502HI_________________________S1VZJDWS462094______ /vmfs/volumes/Shared_Storage/VCB/External.vmdk

OR

vmkfstools -r /vmfs/devices/disks/vml.01000000005331565a4a44575334363230393420202020202053414d53554e /vmfs/volumes/Shared_Storage/BCB/External.vmdk

Either way will accomplish the same thing, as any disk identifier can be used. In theory, i could just use “/dev/sda” as well. Regardless, I now have a .vmdk file which I have attached to my VM.

RDMs are extraordinarily easy to create, however, i should re-iterate that creating RDMs to storage devices that are not shared resources can cause HA/DRS/FT issues.

-D

Posted By: Daenks
Last Edit: 27 Oct 2009 @ 08:34 AM

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