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EMC Fibre Channel Storage System Model FC4700 Configuration Planning Guide
Storage-System Hardware
For high availability, a storage system comes with two SPs. The
second SP provides a second route to a storage system and also lets
the storage system use write caching (below) for enhanced write
performance.
Figure 6-5 Shared Storage Systems
There are more examples of storage in Chapter 5.
Storage-System Caching
Storage-system caching improves read and write performance for
several types of RAID Groups. Write caching, particularly, helps
write performance — an inherent problem for RAID types that
require writing to multiple disks. Read and write caching improve
performance in two ways:
• For a read request — If a read request seeks information that’s
already in the read or write cache, the storage system can deliver
it immediately, much faster than a disk access can.
• For a write request — the storage system writes updated
information to SP write-cache memory instead of to disk,
allowing the server to continue as if the write had actually
completed. The disk write occurs from cache later, at the most
expedient time. If the request modifies information that’s in the
cache waiting to be written to disk, the storage system updates
the information in the cache before writing it; this requires just
one disk access instead of two.
EMC1810
Adapter
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Server
Adapter
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Storage system
SP A
SP B
Storage system
SP A
SP B
Path 1
Path 2
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