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Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

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Cascaded SRDF with EDP

SRDF/Extended Distance Protection (EDP) streamlines cascaded SRDF linkage to the R2 with a diskless R21 device.

With EDP, replication between the R1 and R2 does not require disks at R21 site.

Figure 1. Cascaded SRDF with EDP

Without EDP, the R21 disk device has its own local mirrors so there are three full copies of data, one at each of the three sites.

With EDP, the R21 diskless device has no local mirrors.

Thus, there are only two full copies of data, one on the R1 disk device and one on the R2 disk device.

When using a diskless R21 device, changed tracks received from the R1 mirror are saved in cache until these tracks are sent to the R2 disk device. Once the data is sent to the R2 device and the receipt is acknowledged, the cache slot is freed and the data no longer exists on the R21.

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