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





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