Mount NFS in-guest or in ESXI

[wvladik]

I have a question to all Virtualization admins out there. For the longest time, we have one centOS VM which team of roughly 10-15 techs use as a test machine for various tasks (multicast reciever, wireshark analysis etc.. )

The VM env and the OS is set up is this:
2 x ESXi hosts in HA cluster
1 x NFS NAS host (qnap 16 disks in raid 6)

These 3 devices are connected via 1Gb links to Cisco 4948 switch.

VM has one disk in ESXi (CentOS.vmdk, the core OS and application binaries such as Wireshark, in-house developed multicast processor etc ..) and its location is on the qnap NFS
+
user home folders are presented via NFS in-guest mounting (which is on the same qnap)

My question is, are we paying any performance penalty by not mounting home folders directly in ESXi but in the guest ?

My suspicion is that already NFS mounted OS and then mounting frequently used NFS storage in-guest is sub-optimal but I've been told that is not the case.

I wonder what are others doing and your opinion ?

 

[StammesOpfer]

Not an expert but it seems to come down to which abstraction layer is more efficient the Storage or Network abstraction. If storage virtualization is faster than you would want NFS handled in ESXi and storage passed into the VM. If network is faster then you want the VM to handle the NFS. My gut would say there is probably less overhead on the network side and the CentOS may even have a better implementation of NFS than ESXi. This is based on no real knowledge at all just my thoughts.

 

[wvladik]

while i understand that most of the CentOS lives in the ESXi's host memory (so no system call has to hit the NFS backed storage) there's still some of the OS that is loaded on-demand from the disk.

if that is the case then:
application that lives on OS disk (NFS backed storage) when loading, has to go thru the host CPU/memory -> back to OS disk to load the in-guest mount point -> back to host (the host NIC is where the actual network to NFS lives ) -> back to NFS (in-guest mounted home folder) ..

in contrast, if home folders were mounted by ESXi - the host would handle the calls to the individual disks (NFS mounts)

Ive never done any proper performace investigation and im by no means Virtualuzation expert but i would love to hear what other admins are doing.

Thanks



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