HP Storage Mirroring Software - Manual (Page 101)

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Recovery From Network Losses
Storage Mirroring handles packet losses on the network as well. Storage Mirroring verifies the incoming sequencing before
looking at execution ordering. Here is an example.
1. The source sends packets 1, 2, 3, and 4 to the target.
2. The target receives packet 1. It expects 1, so it passes the operation to the holding/execution handlers and sends its
acknowlegement of packet 1 back to the source.
3. Packet 2 is lost on the network.
4. The target receives packet 3. It expects 2, so it discards packet 3 and resends its acknowlegement of operation 1 to the
source because it was the last successful operation.
5. Because the source already received an acknowledgement for packet 1, it puts any operations that are in the
acknowlegement queue (starting with operation 2) back on the front of the transmit queue to be sent again, in order.
Windows Permissions
If you are using a Windows domain security model by assigning users at the domain level, each user is assigned a security ID
(SID). When Storage Mirroring replicates a file to the target, the SID is also replicated. If you are using a Windows local
security model by assigning users at the local level, users that appear on multiple machines each have different SIDs. After a
Storage Mirroring file and SID is replicated, a local user will not be able to access the file because the user’s SID on the target
machine is different from the SID that was replicated from the source machine.
Storage Mirroring allows you to replicate Windows permission attributes by local name as well as security ID (SID). By
replicating Windows security by name, you can transmit the owner name with the file. If that user exists on the target, then
the SID associated with the user will be applied to the target file ownership. If that user does not exist on the target, then the
owership will be unknown.
By default, Replicate NT Security by Name is disabled. If you are using a Windows local security model, you will need to
enable this feature so that users can access the data on the target.
Task Command Processing
Task command processing is a Storage Mirroring feature that allows you to insert and run tasks at various points during the
replication of data. Because the tasks are user-defined, you can achieve a wide variety of goals with this feature. For example,
you might insert a task to create a snapshot or backup on the target after a certain segment of data from the source has been
applied on the target.
Task command processing can be enabled from both the Management Console and the text clients but can only be initiated
using the DTCL
queuetask command through the text clients.