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18 PS Series Asynchronous Replication Best Practices and Sizing Guide | BP1012
full 10 Gb speed, three times the amount of data is replicated (300 GB compared to 100 GB), but this
replication only takes about twice as long for the three-volume configuration. As the available bandwidth
across the WAN link is decreased, the amount of time to replicate all three volumes increases to where it is
about three times as long. This is because the WAN connection now becomes a limiting factor on the amount
of data the network supports.
Replicating one volume or three volumes
6.3 Effects of thin provisioning
When a thin-provisioned or a regular volume is replicated, only the actual data in use will be copied to the
replication partner. Whether there is a 100 GB volume that is thin provisioned at 10 percent, or a standard
100 GB volume, if only 5 percent of the either volume is filled with data, then only about 5 GB will be copied to
the replication partner in either case. As soon as a portion of the volume is actually written for the first time,
the array will physically allocate disk space, and therefore these changes will be also copied to the replication
partner during the next replication cycle.
For example, when a new Windows NTFS volume is partitioned and formatted, if the quick format option is
chosen, then only a small portion of the disk is actually modified — the master boot record (MBR) — and very
little data will be replicated during the initial synchronization (assuming no additional data has been copied to
the volume yet). However, if the full format option is chosen, Windows will attempt to zero every part of the
new volume, which in turn forces the array to allocate pages from the pool. Even a thin-provisioned volume
will now report that 100 percent of the pages have been allocated (in Group Manager). In this case the
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155Mb (OC3)1Gb10Gb
Replication time (minutes)
Network link speed
Replicating one volume or three volumes
across different speed network links
Three volumes One volume