esxi memory reservations for VM's

edscdk · 25 Sep 2015 at 11:41

we know it greatly increases performance on DB servers, thats fairly easy to test..

has anyone seen any articles or have any experience on weather this is a good idea on citrix / app servers?

IM struggling to find a good article on this, we were considering adding a small reservation across our estate (say 512mb / 1GB) for all server...

skyripper · 25 Sep 2015 at 11:48

It would depend on the app / usage surely. Are there metrics available in ESXi to show how often paging occurs to provide memory to VMs - or two lots of disk IO meter readings, with a Reserved / Not Reserved test?

Reason DB servers work better with dedicated memory is Oracle / SQL Server etc. all like to use as much RAM as possible to reduce the amount of disk IO. It can actively change the execution plan for a piece of SQL when the DB server knows it has more ram and can crunch the results in memory and sort it after rather than sequentially to reduce disk IO.

ASE001 · 25 Sep 2015 at 11:50

edscdk said:
we know it greatly increases performance on DB servers, thats fairly easy to test..

has anyone seen any articles or have any experience on weather this is a good idea on citrix / app servers?

IM struggling to find a good article on this, we were considering adding a small reservation across our estate (say 512mb / 1GB) for all server...

Not sure about citrix but for SQL it can improve performance if memory is over allocated on the ESX host, it stops VMware from paging SQL memory. Paging is bad for SQL servers! So any application where paging is bad then reserve memory.

Mr-White · 25 Sep 2015 at 12:30

You only want to apply the bare minimum memory reservation directly to VMs and not the entire memory amount, ideally you want to have them in resource pool. When applied to a VM, once the memory usage of the server has gone above the reservation VMware can't use memory reclamation to use the memory else where even if the VM isn't using it.

Check whether you have resource contention first as reservations and limits only apply when you do not have enough resources.

MW