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

[nishant mungse]

On Wed, Jan 26, 2011 at 3:04 PM, Malahal Naineni <malahal at us.ibm.com> wrote:

> 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.
>
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Hi Malahal

Thanks for reply. I am not able to understand what  this
"INIT_WORK(&ms->kmirrord_work, do_mirror)" function does. It  is written in
mirror_ctr of dm-raid1. What i think is whenever a bio comes dm_mirror will
be called if that is case then why this is written in mirror_ctr. Please
answer this.

Regards,
Nishant.
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