HP StorageWorks SAN Virtualization Services Platform administrator guide (5697-0109, July 2009)

• Each DPM loses the access to the synchronous mirror storage on the other site. The active DPM
moves the relevant tasks to Failed status and the group to Partial status or Journal status, depending
on mirror mode (Synchronous Always or Automatic Failover).
• If the host that uses the synchronous mirror group is physically located on the same site as the
active DPM, and the synchronous mirror group mode is Automatic Failover, the host I/O operations
continue.
• If the host that used the synchronous mirror group lost connection with the active DPM, it sends a
failover request to the passive DPM.
• If the passive DPM and the active VSM reside on the same site, VSM approves the failover request
and appoints the passive DPM as the new active DPM for that synchronous mirror group. (VSM
approves the failover request because it sees the other DPM as absent.) The DPM then tries to start
the mirror and fails because it cannot access one of the tasks. You must direct the mirror on how
to recover. The synchronous mirror group status is Partial.
• If the passive DPM and the active VSM are not on the same site, the failover request fails, and the
host I/O operations fail. Manual intervention for recovery is expected.
Synchronous mirror failure analysis
1. Find out the actual status of the sites by checking the status of the individual components locally
on each site.
2. If the individual components are online, but the active VSM does not see those of the other site,
then the sites are probably just disconnected. Verify this is the case.
Recovering synchronous mirror volumes from site disconnection
1. Recover the inter-switch link connection between the sites, if possible. Then, initiate a resynchron-
ization (right-click the group, and select Resume) for the synchronous mirror groups after the
restoring the inter-switch link connection.
2. If you cannot recover the connection between sites within a reasonable time, consider appointing
one of the sites as the surviving site and apply the recovery procedure for site failure. Work ac-
cording to Recovering synchronous mirror groups on the surviving site below.
CAUTION:
Do not attempt to partially restore some applications on each site, because it will not be possible to
rejoin the sites back into a stretched domain.
Recovering synchronous mirror groups on the surviving site
If one of the sites is down and cannot be recovered within a reasonable amount of time, you can use
the synchronous mirror task on the surviving site to recover from the site failure. You can recover by
using these procedures:
• Force Resume (see “Recovering the surviving site by using Force Resume” on page 84)
• Force Delete (see “Recovering the surviving site by using Force Delete” on page 86)
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