HP StorageWorks 6000 HP StorageWorks VLS and D2D Solutions Guide (AG306-96028, - Page 187

• Each remote site could have different start time and replication window to ensure target device is not overloaded and best use is made of inter-site link speeds. Device Sizing When sizing a replication target device, the replicated virtual cartridges on the target device take up the same amount of disk space as the original cartridges on the source device, and they also require the same amount of working disk space for deduplication. In other words, if you replicate all of the cartridges in the source device then you need the target device to have the same capacity as the source device. In a many-to-one deployment, add up all the source disk capacity and the total capacity is what you need on the target device. However, the target device is not just adding capacity; it also need to add sufficient extra nodes to handle the replication target disk I/O. With a 24-hour replication window, you need as much node performance on the target device as on the source devices. For example: • With an active-passive deployment, if you have a 4-node/4-array VLS9000 as the source device and you are replicating all of its cartridges, you need a 4-node/4-array target device. • With a many-to-one deployment, if you have four VLS6600/24-disk source devices (which are effectively approximately half a node of performance and half an array of capacity each), you need a 2-node/2-array VLS9000 as the target device. • If you have an active-active deployment, you must combine the required source performance/capacity and the replication target performance/capacity to give you the overall device. If in each site you have a 2-node/2-array requirement for the source piece (i.e., backups), you need 2node/2-array for the target piece. Therefore, you would have a 4-node/4-array device in each site. VLS Replication Data Recovery Options Replication on VLS enables easier recovery of data in the event of a major site disaster. The data is not instantly available but has to be recovered through a standard restore process using a backup application. These scenarios examine what happens with a total site disaster including losing the server and the VLS appliance that was protecting it. In the event of a total disaster at a site where the VLS and the servers it is protecting are destroyed or damaged, the replicated data at the disaster recovery (target) site can be accessed by means of a backup server on the remote site and transferred either to an application or onto physical tape for distribution. Alternatively, when the damaged site is repaired, the most recent backups on the virtual tape library at the disaster recovery site can be restored over the LAN/WAN to the virtual tape library at the previously damaged site. Restore Directly from the VLS Target Device The first method of recovery uses the fact that there are probably more trained IT personnel at the data center and that spare servers, etc., are stored there. With VLS the virtual library containing the replication target (on the target device in the disaster recovery site) is always available through the front-end Fibre Channel ports and thus can be presented as a library to a backup application in the disaster recovery site (note the backup application can only be presented to the target device, it cannot also be presented to the source device as well). HP StorageWorks VLS and D2D Solutions Guide 187