Very slow write speed with LSI raid controller

[ngng72]

I've installed ESXi 5 (updated to the lastest release build 76811)  on a server with LSI 1064E raid controller (raid1 with 2 x 2to sata drive)

With linux I get very decent IO speed (write:>100mB/s, read>150mB/s) on this hardware

But with ESXi the write speed is very lousy (write : 5mB/s, read 50mB)  (results are praticaly the same from the host or inside a vm)

Any ideas ?

Thanks in advance

[a_p_]

Welcome to the Community,

from the speed you mention I assume you don't have a BBU (battery buffered write-cache) option attached to the controller!? Other than Linux or other operating systems, ESXi dos not do software based write caching for data security/consistency reasons, but fully relies on the controller's capabilities. Without BBU the controller operates in write-through mode by default (opposed to write-back with write-cache) which results in the speed you currently see.

André

[admin]

Hi ngng72

Welcome to the communites.

I am agree with a.p , If you need any more information or help pleae letus know.

"Life is never easy for those who dream"

[ngng72]

Thanks for answers and greeting

As far as i know (I rent this server in a data center) there is no bbu, I don't know if the raid card are doing write caching or not (strangely nothing about caching in the raid card bios menu)

Anyway I guess it can't explain such diffence between ESX and linux because all the test has been done in sequential IO with bonnie++ and dd (with big bs and including the time to flush data with "sync" cmd) so os memory write caching don't take into account... and also tryed while mounting hd with sync option

It look like configuration or compatibility issue

[chriswahl]

I've written a post on this subject that may be of some use.

http://wahlnetwork.com/2011/07/20/solving-slow-write-speeds-when-using-local-storage-on-a-vsphere-ho...

[ngng72]

thanks

but It don't seem to be the problem for me because the controller is able to sustain high IO rate under other OS (without using os write cache)

I've just seen on wmware website that support for this chipset is discountinued from ESX v4... that may be the problem...

But If somebody use the same hardware, I would be interested to know how It work for you