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When using an HP StorageWorks P4000 SAN, you would configure a management group at Site A.
This management group consists of a cluster of storage nodes and volumes that serve Site A’s
XenServer resource pool; all VMs rely on virtual disks stored on SRs; in turn, the SRs are stored on
highly-available iSCSI volumes. In order to survive the failure of this site, you must establish a remote
snapshot schedule (as shown in Figure 35) to replicate these volumes to the remote site.
Figure 35. Creating a new remote snapshot
The initial remote snapshot is used to copy an entire volume to the remote site; subsequent scheduled
snapshots only copy changes to the volume, thereby optimizing utilization of the available bandwidth.
You can schedule remote snapshots based on the following criteria:
Rate at which data changes
Amount of bandwidth available
Tolerability for data loss following a site failure
Remote snapshots can be performed sub-hourly, or less often (daily – weekly). These asynchronous
snapshots provide a mechanism for recovering VMs at a remote site.
In any HA environment, you must make a business decision to determine which services to bring back
online following a failover. Ideally, no data would be lost; however, even with sub-hourly
(asynchronous) snapshots, some data from Site A may be lost. Since there are bandwidth limitations,
choices must be made.
Creating a snapshot
Perform the following procedure to create a snapshot:
1. From the CMC, select the iSCSI volume you wish to replicate to the remote site.
2. Right-click on the volume and select New Schedule to Remote Snapshot a Volume.
3. Select the Edit button associated with Start At to specify when the schedule will commence, as
shown in Figure 36.
