HP D2200sb Serial Attached SCSI technology, 3rd edition - Page 7

Storage power management

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Economical, low-power, low-latency, active cables enable high data transfer rates using thinner wire gauges over longer cable lengths. Figure 3 shows: • SAS 1.1 in untrained mode (1.5 Gb/s and 3.0 Gb/s) has a cable length limit of 6 m • SAS-2 in trained mode (both speeds) raises the cable length to 10 m • Active copper cables (6 Gb/s) extends the distance to 20 m • Optical cables (6 Gb/s) extend the distance to 100 m. Figure 3. Comparison of untrained SAS 1.1 and trained SAS-2 with active copper and optical cables Storage power management SAS-2.1 devices can turn off SAS physical links when they are idle. Each SAS transceiver consumes about 200 mW. Turning off all SAS physical links saves a little less than 1 W for a dual-ported drive with two transceivers and a controller (or attached SAS expander) with two transceivers. Table 3 shows more examples of power savings for a 9 W SFF SAS drive. Table 3. Example of power management states for a 9-W SFF SAS drive State Description Commands processed Power savings Recovery time Active Fully active Yes None None Stopped Same as Standby No ~7 W 15-20 sec 7

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Economical, low-power, low-latency, active cables enable high data transfer rates using thinner wire
gauges over longer cable lengths. Figure 3 shows:
•
SAS 1.1 in untrained mode (1.5 Gb/s and 3.0 Gb/s) has a cable length limit of 6 m
•
SAS-2 in trained mode (both speeds) raises the cable length to 10 m
•
Active copper cables (6 Gb/s) extends the distance to 20 m
•
Optical cables (6 Gb/s) extend the distance to 100 m.
Figure 3.
Comparison of untrained SAS 1.1 and trained SAS-2 with active copper and optical cables
Storage power management
SAS-2.1 devices can turn off SAS physical links when they are idle. Each SAS transceiver consumes
about 200 mW. Turning off all SAS physical links saves a little less than 1 W for a dual-ported drive
with two transceivers and a controller (or attached SAS expander) with two transceivers. Table 3
shows more examples of power savings for a 9 W SFF SAS drive.
T
able 3.
Example of power management states for a 9-W SFF SAS drive
State
Description
Commands processed
Power savings
Recovery time
Active
Fully active
Yes
None
None
Stopped
Same as Standby
No
~7 W
15-20 sec
7