On 05/09/2017 05:03 PM, Martin K. Petersen wrote:
Jes,
According to
Documentation/ABI/testing/sysfs-block
Description:
Will always return 0. Don't rely on any specific behavior
for discards, and don't read this file.
See also
Commit: 48920ff2a5a9 ("block: remove the discard_zeroes_data flag")
Crap!
Back to the drawing board :(
Discard is now a deallocate hint like it was originally intended.
Behavior is non-deterministic and no guarantees are made wrt. block
contents on subsequent reads.
To zero a block range you should be issuing blkdev_issue_zerooout().
This will use the best zeroing approach given the device characteristics
(TRIM/UNMAP if the device provides hard guarantees, or regular WRITE
SAME which also does the right thing on some SSDs). If none of the fancy
zeroing commands work, you'll fall back to writing zeroes manually.
Martin,
This is fine within the kernel, however it is not overly useful for
mdadm to determine which strategy to apply when syncing devices.
Jes
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