Re: Searching, but not finding...

[Neil Brown <neilb@suse.de>]

On Mon, 10 May 2010 15:49:20 -0700
Daniel Boggs <BecauseImAwesome@Live.com> wrote:

> Question:
> 
> If I use:
> 
> >>> echo repair > /sys/block/mdX/md/sync_action
> 
> to start a check action, then stop it with
> 
> >>> echo idle > /sys/block/mdX/md/sync_action
> 
> and later start it up again.  Will it start again from the
> "beginning", or is it able to pick up where it left off?

Yes .. if you have a recent enough kernel.

When you write 'idle' you should find the current sector stored in 'sync_min'.
When you write 'repair' again it will start from the value in 'sync_min'.
Obviously if you stop and restart the array you will loose this value unless
you store it in a file somewhere and recover it.


> 
> Essentially if I find the repair/sync action causes too much of a
> performance hit, could I have it run only during hours that I know the
> array will not be in use and still have the array checked in its
> entirety, or is the only way to accomplish that to let the action run
> from start to finish?

You can also reduce the impact by slowing down the scan using sync_speed_min
and sync_speed_max.   'min' is an upper limit to the speed when other IO is
happening, and 'max' is an upper limit when there is no other IO.

NeilBrown


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