Metadata Requirements And Remote Replication - Brocade Communications Systems Brocade 8/12c User Manual

FIGURE 238

Metadata requirements and remote replication

When the metadata and key ID are written, the primary metadata on blocks 1–16 is compressed
and encrypted. However, there are scenarios whereby these blocks cannot be compressed, and the
metadata is not written to the media. If blocks 1–16 are not compressible on the local source
device and metadata is not written, obtaining the correct DEK for the remote target device
becomes problematic. This problem is avoided by reserving the last three blocks of the LUN for a
copy of the metadata. These blocks are not exposed to the host initiator. When a host reads the
capacity of the LUN, the size reported is always three blocks less than the actual size. The behavior
is enforced by selecting the New LUN check box on the Select LUN screen of the Add New Path
wizard when adding LUNs for an SRDF pair (for example, R1 and R2 in
Note the following when using the New LUN option:
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Brocade Network Advisor SAN User Manual
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Basic SRDF configuration with Brocade encryption switches
Both LUNs that form an SRDF pair must be added to their containers using the New LUN
option.
For any site, all paths to a given SRDF device must be configured with the New LUN option.
All LUNs configured with the New LUN option will report three blocks less than the actual size
when host performs READ CAPACITY 10/READ CAPACITY 16.
If a LUN is added with the New LUN option and with encryption enabled, it will always have
valid metadata even if blocks 1–16 of the LUN is not compressible.
LUNs configured as cleartext must also be added with the New LUN option if they are part of an
SRDF pair. This is to handle scenarios whereby the LUN policy is changed to encrypted at some
later time, and to verify formation of DEK clusters and LUN accessibility prior to enabling
encryption for the LUN. When cleartext LUNs are configured with the New LUN option, no
metadata is written to the last three blocks, but will still report three blocks less than the
actual size when host performs READ CAPACITY 10/READ CAPACITY 16.
Adding target disk LUNs for encryption
Figure
18
238).
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