[dm-devel] Improving dm-mirror as a final year project

[Malahal Naineni]

nishant mungse [nishantmungse at gmail.com] wrote:
> 
>    hello all,
>    There is one doubt regarding the dm-raid1. As far as i know, in dm-raid1
>    the data is written parallelly� on all the mirrors of mirrorset and if any
>    of the mirror fails to write the data then dm-mirror adds this mirror to
>    fail list by increasing the error count in "fail mirror" function in
>    dm-raid1.
>    Actually my doubt is where this error count is decremented? i.e after
>    kcpyd or before and where exactly this error count is decremented?

There is no actual 'fail list' of mirror legs. The error_count is never
decremented. The 'error_count' is only used to tell if the mirror leg
has encountered errors. The only way to clear that counter is
re-loading the table!

See the comment:

        /*
         * error_count is used for nothing more than a
         * simple way to tell if a device has encountered
         * errors.
         */
        atomic_inc(&m->error_count);

Hope that helps,
Malahal.