18 Posts
0
484
Data Reduction vs. Hyper-V CSV Free Capacity
Hi,
We have a Unity SAN with Data Reduction enabled for LUNs. This is showing for example as 25% used capacity on the SAN itself, however the actual CSV in Failover Cluster Manager is reporting about 7% free because presumably it is not aware of compression being used on the SAN/LUN itself.
This seems like a massive bug to me, in the Hypervisor! As we are monitoring the Hyper-V hosts for utilization we are getting alerts all the time for something that isn't even a problem.
Is there a solution to this? This is not unique to a single LUN/CSV pair. Disk Management on the LUN and the CSV are both reporting the correct total capacity in FCM.
I'm usually pretty good at Google but don't seem to get the right search expression for this issue to return anything useful.
Thanks
DELL_ChrisHolloway
125 Posts
0
March 15th, 2023 03:00
My answer here may help: https://www.dell.com/community/Unity/unity-350F-with-vmware-compressed-datastores/m-p/8355254#M6035
That question related to ESXi, but the same applies to Hyper-V (except the part about VSI). The OS won't see the backend data reduction saving. However, since everything is thin provisioned just make the LUN bigger, it won't consume any additional space at the backend and the OS will be happy since it now has more free space.
DELL-Sam L
Moderator
Moderator
•
7.1K Posts
0
March 14th, 2023 14:00
Hello ldoodle,
I am not aware of any solution for this issue. What I would do is to double check to make sure you are following the best practices that are listed in this guide. https://dell.to/3leEA5X
ldoodle
18 Posts
0
March 14th, 2023 16:00
Hi Sam,
Thanks for the response and link. I will review and double check. However the kit (Hyper-V physical hosts, Windows OS + Hyper-V configuration, and Storage) was all installed by Dell direct so I would expect it to be to their own best practices.
This seems like a massive disconnect between Microsoft (possibly VMware also if it's the same there) and Storage vendors offering compression/dedupe. This is basic stuff really... and this basic stuff should just work. If a CSV in Hyper-V gets too low it will go offline causing an outage of that data. I am imagining this is based on what Windows reports, rather than what the Storage appliance reports, which is not good news in this scenario. Having compression/dedupe becomes totally pointless if I have to size a LUN at 5X the actual required amount to keep Windows from complaining.
I would actually be very interested in knowing the reason for this oversight.
Thanks again
ldoodle
18 Posts
0
March 15th, 2023 03:00
I've reluctantly accepted that as the answer since it seems there is no other way. This is just really bad from 2 technology powerhouses.
It's a workaround. Not a forever solution. Needs to be fixed.