VM Write Latency

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Hello,

 

I have lot of “VM Write latency” on a new vSAN infrastructure :

  • Version 7.0
  • Full Flash
  • 7 hosts (Dell poweredge 740xd)
  • de-duplication and compression are off

 

Actually, the no traffic on the infrastructure.

 

I use this command to generate benchmark :

[root@a ]$ dd if=/dev/zero of=/test_io/test-24Go bs=1G count=24  iflag=fullblock oflag=direct;

24+0 records in

24+0 records out

25769803776 bytes (26 GB, 24 GiB) copied, 45.7959 s, 563 MB/s

 

The VM where I launched the command is configured like this :

  • Centos 8
  • 2 CPU
  • 2 Go RAM
  • NVME Controller
  • RAID 1

 

The graphs :

Screenshot from 2020-09-09 17-55-47.png

Screenshot from 2020-09-09 17-56-04.png

 

On the backend :

Screenshot from 2020-09-09 17-56-34.png

Screenshot from 2020-09-09 17-56-47.png

 

Host network :

Screenshot from 2020-09-09 17-59-35.png

Screenshot from 2020-09-09 17-59-46.png

 

If I configure the VM in RAID 0, I have no issue and it’s more fast :

[root@a ]$ dd if=/dev/zero of=/test_io/test-24Go bs=1G count=45  iflag=fullblock oflag=direct

45+0 records in

45+0 records out

48318382080 bytes (48 GB, 45 GiB) copied, 63.9457 s, 756 MB/s

 

Any idea ?

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