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RE: [dm-devel] DM does not activate the paths if there are more than one path in path group during failover



Thanks for the response.

If pg_init is intended to be called only once then problem is elsewhere.

During the pg_init, the activate_path is called. The activate_path calls scsi_dh_activate(then rdac_activate) which will set path state to active(h->state = RDAC_STATE_ACTIVE;). My understanding is, h->state is specific to each path. How does d-m sets h->state to RDAC_STATE_ACTIVE for all the paths available in the path group.

This is what happening in my case. On path group failure, d-m switches the path group initiates path group. It then selects the first path (in the path group) starts I/O. After exhausting the repeat_count it then selects the next path in the path group.  Then rdac_prep_fn is called. This function finds h->state is still passive and fails the path which becomes unusable.

This function returns BLKPREP_KILL which is leading to fail failure.

static int rdac_prep_fn(struct scsi_device *sdev, struct request *req)
{
        struct rdac_dh_data *h = get_rdac_data(sdev);
        int ret = BLKPREP_OK;

        if (h->state != RDAC_STATE_ACTIVE) {
                ret = BLKPREP_KILL;
                req->cmd_flags |= REQ_QUIET;
        }
        return ret;
}

This is my understanding so far. Please correct me if there is anything wrong.


-----Original Message-----
From: dm-devel-bounces redhat com [mailto:dm-devel-bounces redhat com] On Behalf Of Alasdair G Kergon
Sent: Monday, November 10, 2008 6:59 PM
To: device-mapper development
Cc: andmike linux vnet ibm com; linux-scsi vger kernel org
Subject: Re: [dm-devel] DM does not activate the paths if there are more than one path in path group during failover

pg_init is a function intended to be called *once* when there is a switch to a new group of paths.  It is not per-path initialisation.

Alasdair
--
agk redhat com

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