EMC Symmetrix DMX-3 User Manual

Elements of a Symmetrix I/O operation
105
Symmetrix DMX-3 Input/Output Operations
Elements of a Symmetrix I/O operation
All I/O operations require a certain response time. An I/O request
begins when the application issues an I/O command and ends when
the data transfer completes. The time interval from I/O request to
transfer completion is the I/O response time.
This section describes:
◆ “I/O response time: Mainframe environment” on page 105
◆ “I/O response time: Open systems environment” on page 106
◆ “Symmetrix I/O operations” on page 106
◆ “Read operations” on page 108
◆ “Write operations” on page 110
◆ “Write destaging operation” on page 112
I/O response time:
Mainframe
environment
In the mainframe environment, I/O response time can be divided
into a queuing time, a pend time, a connect time, and a disconnect
time, as shown in Figure 21 on page 105.
Figure 21 I/O response time (mainframe environment)
The Queuing time is the I/O Supervisor (IOS) queue for next the
event.
The Pend time consists of:
◆ Control Unit Busy (CUB)
◆ Device Busy (DB)
◆ Director Port Busy
The Connect time is the length of time the channel processes
commands and transfers data.
The Disconnect time is:
◆ The length of time it takes to retrieve data from the physical disk
(device seek and latency)
◆ The length of time it takes to reconnect to the host
◆ SRDF write overhead (protocol, line latency, and so on)
Queuing
time
Pend
time
Connect
time
Disconnect
time
Device service time
I/O response time

EMC Symmetrix DMX-3 Specifications

General

Brand	EMC
Model	Symmetrix DMX-3
Category	Storage
Language	English