Memory assignment for VM

I see a article about a custom memory reservation :


"default reservation of 0MB means the ESX/ESXi host does not have to provide the virtual machine with any physical memory. The virtual machine get its memory with VMkernel swap. VMkernel swap if a file created when a virtual machine is powered on with a .vswp extension. By default, this file will be equal to the size of the RAM that you configured the virtual machine. A virtual machine can get its memory allocation entirely from VMkernel swap – or disk – resulting in virtual machine performance degradation."

So, should it set the the memory reservation value rather than leave it as default, ie 0 ?

Tks
AXISHKAsked:
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szichenCommented:
You don't have to reserve the memory unless this is a critical server and the host has multiple VMs that may cause resources to become low at times.
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AXISHKAuthor Commented:
Here is the current memory usage on the ESXi server.
 
# esxtop
 3:29:16am up 2 days  1:54, 492 worlds, 7 VMs, 17 vCPUs; MEM overcommit avg: 0.67, 0.67, 0.67
PMEM  /MB: 20477   total:  1284     vmk, 15979 other,   3214 free
VMKMEM/MB: 20377 managed:   735 minfree,  4860 rsvd,  15517 ursvd,  high state
PSHARE/MB: 11802  shared,  1251  common: 10551 saving
SWAP  /MB:   813    curr,   152 rclmtgt:                 0.00 r/s,   0.00 w/s
ZIP   /MB:    61  zipped,    37   saved
MEMCTL/MB:  7050    curr,  7050  target, 20997 max


◦MEMCTL: displays the memory balloon driver statistics.
Does it mean the server encounter shortage of memory, as I see the maxium MEMCTL/MB has logged with 20GB ?

Tks
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
You ONLY need to set a memory reservation IF YOU WANT TO RESERVE memory, or GUARANTEE MEMORY for the VM.

So, do you have other VMs, on your host?

Are you short of memory on the host?

If the answers are no, to the last question, there is no real benefit of providing a memory reservation.
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AXISHKAuthor Commented:
Tks, but for the

◦MEMCTL: displays the memory balloon driver statistics.


Does it tell me whether the memory is sufficient or not ?

Tks
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
The balloon driver, is only expanded if memory is short on the host, and it needs to reclaim memory from the Virtual Machine.

see here

http://www.vfrank.org/2013/09/18/understanding-vmware-ballooning/
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AXISHKAuthor Commented:
Tks. Does the static indicate a memory shortage in host where I need to add more memory ?

Tks again.
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AXISHKAuthor Commented:
Thx
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