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http://www.aidanfinn.com/?p=19043

How do you calculate reserve for host to run smoothly ? is really like the website ?

so if i have 768 GB RAM then i can use 750 GB just for VM and run smoothly at 99% ram usage without any problem ? (So the host only used 28 GB ?)

Davin Dirgantara
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Pretty much yah. eck, even more. Depends how yo ucalculate VM usage

RAM on the host is used for:

  • The host OS.
  • IO caching (which the VM's also do)
  • Overhead for VM's

Generally the last is like 1gb per VM... max... so... yeah... your numbers are conservative, actually.

If you run a modern hyperconverged setup you may want to have some more RAM for the CSV cache.

BaronSamedi1958
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TomTom
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  • so the website is legit ? any source from microsoft maybe you have or any guidebook... – Davin Dirgantara Mar 15 '18 at 08:48
  • Common sense. There i an overhead per VM an there is some space the host needs, but normally it ONLY runs hyper-v, so it wont really grow too much. Also remember that this is not 99% usage in your example, it is 99% allocation - which makes sense. Usage is then whether or not the VM acutally uses it. – TomTom Mar 15 '18 at 08:52
  • so recommended ram usage within 95 % for vm only and 5 % only for host will be okay with that spec 768 gb you think ? sorry if asking it too trivial... – Davin Dirgantara Mar 15 '18 at 09:39
  • I personally think you really give the host too much, particularly for only one VM. The host likely can handle with only 8gb for it's operation. unless you use CSV caching, Hyper-V io is not cached on the host. – TomTom Mar 15 '18 at 09:59
  • okay then, 768 total. 700 used for vms and 68 for hyper v windows server 2012 seems really safe right, thanks man – Davin Dirgantara Mar 15 '18 at 11:59
  • It's not one vm, i have many vms for db, apps, management, etc. the total usage of all vm is 700gb which leaves for hyper v 68 gb... it's still in the rule right ? – Davin Dirgantara Mar 16 '18 at 05:59
  • Well, as I said: I generally deduct 1gb overhead per VM, plus a handfull (max 8) GB for the OS. On a S2D CSV I add some more to the CSV cache - 1gb per VM again. That has served me well so far. – TomTom Mar 16 '18 at 08:59
  • Can i ask again about a good book for resource management in all virtualization platform ? thank you in advance and your guidance – Davin Dirgantara Mar 19 '18 at 04:12
  • S2D can't use RAM as a cache, I've removed wrong information from text marked as "answer". – NISMO1968 Mar 24 '18 at 17:01