register
Contributor
Contributor

question about the size of the RDM mapping file

3.5 update3

I must be misunderstanding RDMs. I thought I could create a LUN on my SAN, then VMWare would create a small RDM mapping file on a VMFS store that acted as a pointer to the real LUN. I've created a few test RDMs (200 -400 MB), and VMWare is always creating a "servername-rdmp.vmdk" file that matches the size of the LUN. If this is the case, in order to use a 100 GB RDM, I will need 100 GB on my SAN + 100 GB of free space on my VMFS volume for the RDM mapping file. This can't be right. I'm assuming that the *-rdmp.vmdk files are not actually taking up that much space. How can I find out how much space they really use?

thank you

0 Kudos
4 Replies
weinstein5
Immortal
Immortal

It is misleading - the actual size of the file is small but when viewed through the vi client browser - it will show the RDM as the size of the LUN 0 if you got to the cli you sill be able to use the ls command to see the tru size of the RDM -

If you find this or any other answer useful please consider awarding points by marking the answer correct or helpful
0 Kudos
register
Contributor
Contributor

ls -h is what I'm using to check the size. It shows a 400 MB file.

0 Kudos
sbeaver
Leadership
Leadership

I forget how to prove otherwise off the top of my head but the mapping file itself is only a couple of megs if that

Steve Beaver

VMware Communities User Moderator

====

Co-Author of "VMware ESX Essentials in the Virtual Data Center"

(ISBN:1420070274) from Auerbach

*Virtualization is a journey, not a project.*

Steve Beaver
VMware Communities User Moderator
VMware vExpert 2009 - 2020
VMware NSX vExpert - 2019 - 2020
====
Co-Author of "VMware ESX Essentials in the Virtual Data Center"
(ISBN:1420070274) from Auerbach
Come check out my blog: [www.virtualizationpractice.com/blog|http://www.virtualizationpractice.com/blog/]
Come follow me on twitter http://www.twitter.com/sbeaver

**The Cloud is a journey, not a project.**
0 Kudos
jsykora
Enthusiast
Enthusiast

The *-rdm.vmdk mapping file you see on your VMFS volume is just a placeholder and really small even though it shows up as the same size as the RDM. I'm not sure exactly how to see the actual size of the file either.

I did want to add that you do need to make sure you have some space available on the VMFS volume for snapshots though as any snapshot delta files for the RDM will go to the VMFS file where you .vmx is located.

0 Kudos