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EMC Symmetrix DMX-3 Product Guide
Symmetrix DMX-3 Input/Output Operations
Write operations
Symmetrix systems use large global memory configurations, and 100
percent global memory fast writes to ensure the highest possible
performance when writing data. Symmetrix systems write operations
occur as either fast write or delayed fast write operations (Figure 23
on page 107).
Fast write A fast write occurs when the percentage of modified data in global
memory is less than the fast write threshold. On a host write
command, the channel director places the incoming blocks directly
into global memory.
For fast write operations (Figure 27 on page 110), the channel director
stores the data in global memory and sends a channel end and device
end (or a SCSI good ending status) to the host computer. The disk
director then asynchronously destages the data from global memory
to the disk drive.
Figure 27 Write operations
Fast write also allows Symmetrix systems to accommodate bursts of
writes at a speed above and beyond the speed that the hard drives
allow. The negative effects of bursty writes are minimized through
this algorithm.
Channel
Channel
director
Global
memory
Disk
Asynchronous
destage
Fast write
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