Managing HP X9000 Network Storage System Remote Replication Application Note (TA768-96049, November 2011)

1 Using remote replication
X9000 remote replication is a file-based solution that replicates changes in a source file system
on one cluster to a target file system on either the same cluster (intra-cluster replication) or a second
cluster (inter-cluster replication). Remote replication is asynchronous and runs in parallel across the
cluster. Both files and directories can be replicated, and no special configuration of segments is
needed.
An X9000 system can be a source for one replication task and a target for another task, allowing
you to implement one-many, many-many, and many-one replication solutions.
Overview
Replication modes
The replication modes apply to both intra-cluster and inter-cluster replication.
Continuous replication
This mode tracks changes on the source file system and continuously replicates the changes to the
target file system. The changes are tracked for the entire file system and are replicated in parallel
by the file serving nodes.
Use continuous replication when you want to keep the source and target synchronized. Remember
that X9000 replication is asynchronous and some files on the target may not be up to date if data
was in transfer at the time of a disaster.
Continuous replication tries to replicate on a first-in-first-out basis, but there is no strict order to
replication at either the file system or segment level. There is no concept of “in-order delivery” or
“consistency groups,” which are common features of block-based replication solutions.
When you configure continuous replication, you must specify a file system as the source. You can
specify either a file system or a directory as the target.
Run-once replication
This mode replicates a single directory subtree or an entire file system from the source file system
to the target file system. Run-once replication makes a single-pass of all files and subdirectories in
the specified directory or file system. All changes that occurred since the last replication task are
replicated from the source file system to the target file system.
Use run-once replication for bulk copying of files, when a point-in-time copy of a source is required
on a target, and for replicating native file system snapshots.
Replication sources
Depending on the replication mode, sources can be whole file systems or directories. When
selecting file systems for remote replication, be aware that:
• You can replicate one, multiple, or all file systems in a single cluster.
• Remote replication is a one-way process. Bidirectional replication of a single file system is not
supported.
• The mountpoint of the source file system can be different from the mountpoint on the target
file system.
• Targets must be treated as read-only. Although this requirement is not enforced by the X9000
software, it can be enforced at the protocol layer by exporting or sharing read-only.
4 Using remote replication