On 13/08/18 11:56, Reindl Harald wrote:
"Two threads writing with O_DIRECT io to the same address could result
in different data on the two devices" makes no sense - everything talks
with the RAID1 layer which is a block-device and expected to have alway
the same data on both mirrors - O_DIRECT don't bypass the RAID layer
because it even don't know about the phyiscal disks underneath
if what ever workload (except a hard crash) leads to different data it's
a bug which should be fixed better sooner than later
Sounds to me like it's worse than that - IN NORMAL OPERATION it sounds
like it could return different data from different reads of the same
section of the file!
What's it called - "the principle of least surprise"?
If I write to block 658 of the raid-1, then surely it should be written
to block 658 (plus house keeping offset) of *both* underlying devices.
Otherwise you need a translation layer to say which raid block is which
device block on which raid device. Of course, that could be the
bad-blocks layer.
And if that translation layer is messed up, then you get a corrupt raid.
That's a point, though. Does the raid we are discussing have a bad
blocks layer?
Cheers,
Wol
