HP StorageWorks SAN Virtualization Services Platform Manager user guide (AG781-96017, March 2009)

The mirror service enables you to specify the number of PiTs to maintain on the source domain, per
group, and the number of PiTs to maintain on the destination domain, per task. When a new PiT is
created on a source or destination, an old PiT is deleted if the new PiT increases the total number of
PiTs to a higher number than the maximum permitted. Standard PiTs are deleted before user PiTs.
Older PiTs are deleted before newer PiTs. You can release user PiTs from their special status as user
PiTs so that PiTs are only deleted in order of age.
Since a PiT can grow to the size of the virtual disk on which it is created, the storage capacity is a
consideration when deciding how many PiTs to maintain on each domain. On the destination, a
greater number of PiTs provides more recovery possibilities. Having more PiTs on the source increases
the recovery possibilities but may affect application performance because of the extra overhead in
maintaining more PiTs.
You can check the consistency of data on a destination by generating a snapshot on a destination
PiT and mounting the snapshot on a host. If you create a snapshot on a destination PIT, that PIT cannot
be deleted. In this case, the number of PiTs on the destination can grow to be greater than the
configured limit.
The mirror service offers features called detach, split, and merge that enable you to switch the mirroring
direction (for example, failover) between domains. The domain that is originally the destination domain
of a group can become the active domain and can then mirror data to the domain which was originally
the source domain. The mirror service resumes the process from the cut-off point without having the
need to start the mirroring from scratch. The procedure is useful both for a planned switch over and
an unexpected switch over which is a result of primary site failure.
Viewing asynchronous mirror groups
You can view all async mirror groups for which the local domain is either the source domain or the
destination domain in the async mirror groups list.
Viewing groups for which the local domain is a destination domain enables you to easily locate
mirrored virtual disks in case you need to use them for recovery.
To display async mirror groups:
In the navigation tree, click the Async Mirror Groups node. The async mirror groups list appears in
the list area. The following information is displayed for each group.
Table 108 Async mirror groups properties
DescriptionProperty
The row number.No
The name of the async mirror group.Name
The name of the source element defined by the group. This may be a virtual disk,
a snapshot, or a VDG.
Source Name
The source domain of the group.Source domain
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