Advanced parameter Disk.DiskMaxIOSize ???

[eric00]

Customer has ESX 4 hosts.  they have all of their servers set with advanced parameter = Disk.DiskMaxIOSize set to 32.  The default value is 32767.

I can't find documentation on this parameter.  Does "32" make sense, or, are they throttling their I/O to a 32-byte block size???

Thanks,

Eric

[AndySimmons]

That value is in KB, but yes, they are limiting I/O requests to 32 KB. Default is 32 MB. Some storage devices run into performance issues with I/O requests over a certain size, although 32 KB seems really small. I would check with the SAN vendor to see what they recommend.

Here's a KB article with some details.

[depping]

I would in general recommend tweaking advanced settings UNLESS you have clear directions from VMware support or your storage vendors support. I have seen some vendors (HP with the EVA for instance) recommending a lower "Disk.DiskMaxIOSize". usually in the course of 128 / 256. I had not seen 32 yet to be honest.