Memory reservation question

[Bruticusmaximus]

We have a huge SQL VM that we run by itself on a host.  No other VMs running on it.  The host has 1 TB of RAM.  The VM has 512 GB of RAM.  Someone posed this question to me "Would there be any benefit of reserving all 512 GB on the VM?". 

There is no intention of ever running any other VMs on this host. We're not planning on increasing the RAM of the VM.

One downside I see is that if this VM has to fail over to a host that does have other VMs running on it.

Is there any upside to doing this?

What are your thoughts?

[nparas5]

If you reserve the memory and suppose if SQL VM needs more memory (Some PeakTime) than the reserved then you could have performance problems on the VM itself if there are other VMs in the host as well. And if SQL person is assure that its utilization will be under 75% threshold everytime then no need for any reservation.

And if the host is in DRS cluster it will try to migrate the other VMs on this host to keep all the host in cluster balanced. Reservation is only need in order to avoid Memory over commitment, and as said below you have the single VM on the host, it will not change impact anything if you do reservation or not.

[batuhandemirdal]

Hi,

Cluster features vsphere DRS true ?

[senthilkumarms8]

Yes, the VM will get performance benefit if you are doing full memory reservation. Because the memory reservation will allocate the continues memory pages to the guest OS. so the database table indexing and SQL Server in-memory OLTP helps to improve performance.However, i suggest you look at the physical NUMA architecture before doing such CPU/Memory reservation.

the second point here to notice is that we required 512GB of free memory in another host when there is an active host failure.