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File Server iSCSI Volumes - In Guest vs RDM vs VMDK?

Question asked by James Moth on Feb 11, 2016
Latest reply on Aug 31, 2017 by noam

Hi, I'm trying to determine the best way of connecting my iSCSI volumes and struggling to find clear answers.


I'm currently using a 2012R2 File Server with 3 iSCSI Volumes consisting of 2.6TB, 2.5TB and 1.5TB. These are currently connected "The old fashioned way" aka in guest iSCSI.


However I have a few issues, the server has deduplication enabled and initially the space savings are reported back to the Nimble ok, but when either a backup or garbage collection (I'm unsure which is causing this) runs on the weekend the deduplication savings are lost to the Nimble but eventually return after a few days. Given the fact that the deduplication is unreliable in reporting space savings, it's not technically saving me any space. Would changing from in guest iSCSI to either RDM or VMDK produce any different or hopefully more reliable results from this aspect? What are the pros and cons of each?


Secondly in terms of backups, if i changed to a VMDK for example i could then make use of Arcserve UDP to backup and snapshot the data, but are VM snapshot backup softwares reliable with this quantity of data or would i be better off continuing to use Arcserve Backup for that aspect? I know there was some concern about that quantity of data back in vSphere 4 days which is why we opted to set it up with in guest iSCSI i think, but I'm now running vSphere 6.