I am trying to modify read ahead value using blockdev. When I issue this command blockdev --setra xxx /dev/sda - it changes the readahead value of the entire partition in that device, which is fine. But when I went to any of the partition in that device and check inode_readahead_blk value under /sys/fs/ext4 folder, I don't find the same readahead value I changed earlier using blockdev. I am little confused about this. Would any one of you cast some light on this one please? 
Changing readahead value using blockdev command
linux;block device;ioctl