American Megatrends ManageTrends 2.7, Руководство пользователя

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Appendix E : Replication Overview 243
Multi-level link scheduling enables StorTrends to transfer data efficiently across the IP
link. Built-in smarts in the stack permits the replication module to intelligently skip
snapshots when the lag exceeds threshold due to excessive I/O load on the Production
Server. The replication data from fine-grained delta-snapshots are optionally further
compressed to push out minimal data packets over the link. Depending on the load in the
system, the compression algorithm varies the depth of compression to ensure most
optimal balance between the CPU and Link utilization.
A background patrol task can be scheduled that checks the correctness of replication by
using CRCC validation across the two sites. This provides additional insurance without
consume any additional link bandwidth. Unlike most of the present day Storage-servers,
StorTrends offer intuitive wizards to assist in Fail-over, fail-back and rollback in the
event of a disaster.
Delta snaps
In Snap assisted replication, always only the difference between the old and new snapshot
is replicated to the secondary – essentially these are the new data written during the new
snapshots life cycle. These delta data between the snapshots will be written directly to the
volume on the secondary and once all delta data for a particular snapshot are replicated, a
snapshot will be taken on the recovery site. The snapshots in the secondary are essential
to provide recovery points.
In the event of a failover, the active volume in the secondary cannot be used as it may
have some snapshot data that is NOT fully consistent. On a failover to secondary system,
the StorTrends iTX will automatically rollback to the latest available snapshot in the
secondary. This provides a consistent image to start with upon a failover in the secondary
system.