topic Re: VSC 4 and RCU in VMware Solutions Discussions

VSC 4 and RCU

bazmercer — Thu, 05 Jun 2025 06:18:10 GMT

Hello,

Could someone help me out here with the RCU please. I'm trying to do an RC of a vm template. Currently it's thickly provisioned on the NFS store. When I clone it and no matter what option I select of "leave in the same format" "thin provison" or "thick provision" the VSC does an initial copy of the image. This seems like a complete waste of time to me, why doesn't it just clone the original template? Is there a way to avoid doing this initial copy or at least speed it up? Copying the 40gb takes quite a while.

this is my first time with the RCU so it may well be that I don't understand the concepts of it. At one point, it did do a very quick clone of the template but now it seems to do an entire file copy. Is this expected?

Thanks

Re: VSC 4 and RCU

bazmercer — Fri, 28 Sep 2012 11:14:07 GMT

To add, when leaving "same format as source" it appears to do a clone into a new directory in the datastore called "ntap_rcuxxxx". However, it then deletes it, creates a directory called ".tmpndmpdir" and does a copy of the template. Confused!

Re: VSC 4 and RCU

costea — Fri, 28 Sep 2012 13:34:51 GMT

What you're describing sounds like RCU fell back to using an ndmpcopy for the first clone rather than immediately doing a sis-clone. This will happen if you are cloning from one volume to another or if you have exhausted the max shared blocks limit. This limit is 255 in ONTAP 7.3 and 8.0. Once a block within the source file has been deduped 255 times, a new copy must be created. RCU does this by cancelling the clone operation and falling back to an ndmpcopy. There are preferences that allow you to prevent this fallback detailed in the IAG.