[CentOS] Avago (LSI) SAS-3 controller, poor performance on CentOS 7

For the archive's sake:

https://plus.google.com/+GordonMessmer/posts/H5DuyP1LHPU?sfc=false
https://plus.google.com/+GordonMessmer/posts/eSe6iNmk1Fs?sfc=false

During testing, I found that under CentOS 7.2, the default storage 
layout for software RAID5 was the worst possible configuration. 512k 
blocks perform noticeably worse than 64k blocks, and LVM had a 
tremendous impact as well.

After upgrading to CentOS 7.3, which features a newer mpt3sas driver, 
performance improved significantly.  LVM's overhead has decreased to an 
acceptable level (from my point of view).

Because chunk size has a significant impact on performance, I'm going to 
file an RFE to change the default chunk size for RAID5 and RAID6 volumes.