March 2013
Dell EqualLogic Configuration Guide v14.1
6-54
Table 22
Comparing SyncRep and traditional replication
Replication
consideration
Traditional replication
SyncRep
Typical Use
Case
A point-in-time process that is conducted
between two Groups, often in
geographically diverse locations.
Replication provides protection against a
regional disaster such as an earthquake or
hurricane.
Traditional replication has the advantage of
providing multiple recovery points.
A disadvantage of traditional replication is
that the state of the data between recovery
points is unknown; if any changes are
made to the volume since the last replica
was created, they could be lost.
A real-time process that keeps two
identical copies of volume data in
two different pools within the same
PS Series group.
SyncRep is useful for maintaining two
copies of a volume's data in the same
data center, or dispersed to two
different facilities on the same
campus or in the same metropolitan
area.
An advantage of SyncRep is that it
captures a duplicate copy of every
write. One disadvantage of this is that
if an application writes bad data to
the volume, the bad data is
simultaneously written to both the
SyncActive and SyncAlternate pools.
Recovery Time
If a disaster occurs in the primary group,
you can promote the replica set on the
secondary group to a recovery volume.
After the promotion, you must reconfigure
initiators to discover and log in to the iSCSI
target now hosted by the secondary group,
or switch to an alternate set of server
resources that have been preconfigured to
use the secondary group storage. See the
Impact on Applications row of this table for
more information.
If a disaster involving the SyncActive
pool occurs, you can manually
switch the volume to the
SyncAlternate pool.
After the switch, the SyncAlternate
pool becomes the SyncActive pool
and hosts the volume.
Host access to the volume is
disrupted by the switch, but iSCSI
initiators do not need to be
reconfigured.
Recovery Point
The recovery volume contains point-in-
time data that is current as of the most
recent replica. Replication can be
scheduled to take place as frequently as
once every five minutes.
You can also restore to the point in time
when any previous replicas were created,
provided that the replicas have been
retained.
SyncRep provides a single recovery
point: the most recent
acknowledged write to the volume.
