Vsan Policy FTT and performace

[SoheilAmiri]

hello guys

i am setting up 4 vSAN host with 120gb (host) + ( 2*500gb) all flush drive in a lab.

 i have some question : 

1-for having a baseline value  i install ESXi on one stand alone host ( HDD config : 120Gb WD for host  + 500gb Samsung for VM) with no RAID configuration. create a Ubuntu VM on 500Gb HDD and run disk benchmark. result is :Read: 540 MB, Write: 362 MB

2- i create a vSAN cluster with  HDD config : 120Gb WD for host  + (2* 500gb Samsung) for vsan cache and capacity tier.

all servers in section 1 , 2 have the same hardware configuration.

i create and ubuntu VM with this policy in attachment and run disk benchmark app again : Read: 1.1 GB, Write: 151.5MB

i except double Read performance as the result show and near single drive write performance. but the result is about 40% performance. do i did something wrong in my configuration ? 

[depping]

Not sure why you would expect that? you are comparing no-raid with a raid configuration which also hits the network? Those numbers will always be different and you can't compare them really to be honest. Look at your vcenter graphs to see where the potential bottleneck is, or use something like HCIBench to do a deeper analysis, but in general you cannot expect the same performance. Also note, depending on the size of the SSDs you may experience a situation where the write buffer needs to destage as it is running out of capacity.

[SoheilAmiri]

hello @depping

thanks for your reply.

here is why think like this way:

- No Raid config host : Read=x MB   Write= y MB

- RAID-1 Mirror config: Read= 2x MB   write=y MB

this theory is correct. am i right ?

i use the default network and vcenter configuration. i use vSAN storage policy to config my vm resiliency ( VMDK object). RAID-1 with 1 FTT. according to my RAID knowledge RAID mirror will not effect write performance in theoretical. i know i will lost some of my performance in real world. here i lost 60% of my performance. does this percentage acceptable or i am miss something ?

[IRIX201110141]

Wrong.

write=z MB

Because z have to go over the wire and even when having enterprise grade networking gear you will see the impact. System have to wait until the IO is confirmed by the other node. Same is true for any Sync. SAN mirror.

Regards,
Joerg

[SoheilAmiri]

thanks 

you are right. i will lost some of my performance because traffic will through the Enterprise network. but it should not impact the performance up to 60% of original  performance.

i guest i must mistake on my configuration. i need a technical guide

[SoheilAmiri · Accepted solution]

hello guys

by enabling HBA mode on HP RAID controller the performance increase , and the write and Read rate improve so much.

 - No Raid config host : Read=x MB   Write= y MB

- RAID-1 Mirror config: Read= 1.7x MB   write=0.8y MB

so nice.

thanks