Re: [Question] why not flush device cache at _vg_commit_raw

Dne 22. 01. 24 v 12:22 Su Yue napsal(a):
> Hi lvm folks,
>    Recently We received a report about the device cache issue after vgchange —deltag.
> What confuses me is that lvm never calls fsync on block devices even at the end of commit phase.
> 
> IIRC, it’s common operations for userspace tools to call fsync/O_SYNC/O_DSYNC while writing
> critical data. Yes, lvm2 opens devices with O_DIRECT if they support , but O_DIRECT doesn't
> provide data was persistent to storage when write returns. The data can still be in the device cache,
> If power failure happens in the timing, such critical metadata/data like vg metadata could be lost.
> 
> Is there any particular reason not to flush data cache at VG commit time?
>

Hi

It seems the call to 'dev_flush()' function got somehow lost over the time of 
conversion to async aio usage - I'll investigate.

On the other hand the chance here of losing any data this way would be really 
really very specific to some oddly behaving device.


Regards

Zdenek