it may be a mess that if there is 2 btrfs partition (1 via bcache, 1 via dm) with same UUID appear at the same time.

https://btrfs.wiki.kernel.org/index.php/Gotchas

Currently, i think removing cache device would be simpler.


On May 12, 2016 7:57:48 AM GMT+08:00, Marc MERLIN [off-list ref] wrote:

On Thu, May 12, 2016 at 07:34:26AM +0800, ching wrote:

quoted

for example

https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs-scrub

btrfs scrub is designed to make sure all the blocks and checksums are
consistent.
Ching makes a good point that it would be helpful to have a way to
access the underlying backing device directly to ensure it is
consistent.

I think currently you can use dmsetup with an offset to get the real
filesystem past the bcache header, mount that read only somewhere and
scrub that.
Not ideal because scrub will not be able to fix issues that are
fixable,
but at least it should report errors.

Would that work?

Marc

quoted

On May 12, 2016 3:13:22 AM GMT+08:00, Eric Wheeler

[off-list ref] wrote:

quoted

quoted

On Wed, 11 May 2016, ching lu wrote:

quoted

The read cache prevent the program to scrub the backing device

directly.

quoted

if a few bits flipped in the backing device, the cache may still
return healthy data for a while.

Must i remove cache device before scrubbing?

What do you mean by scrub?

--
Eric Wheeler

quoted

On Wed, May 11, 2016 at 9:15 AM, Eric Wheeler

[off-list ref] wrote:

quoted

quoted

On Fri, 29 Apr 2016, ching lu wrote:

quoted

Hello,

i want to develop a script to perform data scrubbing

periodically.

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I think you want to set dirty_percent to 0 and

cache_mode=writethrough.

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Then wait a long time for dirty_percent to actually reach 0.

--
Eric Wheeler

quoted

For my use case, i think it is meaningless to scrub cached

data.

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If i change the cache mode to "none", will it turn off the read

cache too?

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Furthermore, will this invalidate cached data? (i do not want

to

quoted

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"warm

quoted

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up" the cache again after the scrubbing)

Thanks in advance,
c
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