Slow file transfer speeds on files over 2gb in size. [ESXI 6.0 (Build 3073146)] - [Supermicro X10SRH-CLN4F-O, LSI 3008]

[AES256]

I've been fighting with getting these file transfer speeds up for a week now.

Using a Windows 2008 Enterprise OS to copy from one drive to another is blazing fast with files under 2GB.  When copying a 7gb file it drops from 600mb/s to 24mb/s when it gets halfway.

I have upgraded the firmware on the LSI 3008 and it did not help resolve this issue.

Does ESXi 6.0 throttle transfers for large files?

[a_p_]

Welcome to the Community,

ESXi doen't throttle the file transfer nor does it provide disk caching, but fully relies on the controller's caching capabilities. Unless I'm mistaken your controller doen't support a BBU option, which is required to have the controller operate in write-back mode rather than in write-through mode!? I guess that the high transfer speed works as long as the target operating system's has cache available for the data. Once the cache becomes saturated, the data has to be written to disk, which likely causes the performance hit.

Not related to your issue, but still important. You may consider to patch your host to resolve a critical CBT issue (see https://esxi-patches.v-front.de/ESXi-6.0.0.html).

André

[JarryG]

You do not write anything about your VM-configuration, but I simply suppose for "small" files your VM has enough free vRAM to be used as disk-cache. As soon as your OS disk-cache is full, speed drops to raw disk i/o-speed. You can follow this in TaskManager ("Performance" tab, size of cached/free memory)

BTW, on-board LSI-3008SW controller is very "basic", with no on-board cache (and thus unsuitable for ESXi-storage, because ESXi does not do disk-caching). 20-30MB/s is quite normal for un-cached disk (or raid0/1 array), especially if it is a little fragmented. You can not expect much more...