[FS#653] RAID not working on Netgear WNDR4700

[LEDE Bugs]

The following task has a new comment added:

FS#653 - RAID not working on Netgear WNDR4700
User who did this - Szabo (kisgezenguz)

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Hi diizzyy, Christian,

thank you for the input.
I set up a Virtual box and compiled the mdadm 4.0, but is not help.
I think also Christian hint will solve this problem,
my question is only: Hot to request to add the CONFIG_KERNEL_DIRECT_IO to the stable release?  

root at Netgear:~# /tmp/mdadm -V
mdadm - v4.0 - 2017-01-09

root at Netgear:~# /tmp/mdadm --create --verbose /dev/md1 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdd1
mdadm: Note: this array has metadata at the start and
    may not be suitable as a boot device.  If you plan to
    store '/boot' on this device please ensure that
    your boot-loader understands md/v1.x metadata, or use
    --metadata=0.90
mdadm: partition table exists on /dev/sdd1
mdadm: partition table exists on /dev/sdd1 but will be lost or
       meaningless after creating array
mdadm: size set to 982464K
Continue creating array? (y/n) y
mdadm: unexpected failure opening /dev/md1

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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=653#comment2246