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Subject: Re: [BUG] Btrfs scrub sometime recalculate wrong parity in raid5:
 take two
To: Chris Mason <clm@fb.com>, kreijack@inwind.it,
        linux-btrfs <linux-btrfs@vger.kernel.org>
References: <da6e9c30-02a0-39fc-3c67-d0af4fd5bf51@inwind.it>
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From: Andrei Borzenkov <arvidjaar@gmail.com>
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Date: Fri, 15 Jul 2016 19:34:38 +0300
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15.07.2016 19:29, Chris Mason пишет:
>
>> However I have to point out that this kind of test is very
>> difficult to do: the file-cache could lead to read an old data, so please
>> suggestion about how flush the cache are good (I do some sync,
>> unmount the filesystem and perform "echo 3 >/proc/sys/vm/drop_caches",
>> but sometime it seems not enough).
> 
> O_DIRECT should handle the cache flushing for you.
> 

There is also BLKFLSBUF ioctl (blockdev --flushbufs on shell level).