Comment 60 for bug 539467

As the pm-utils have the feature disabled, the test case would be:

ls -la /sys/block/sd?/device

Note the link points to h:b:d:l, where h is the host number. Then change into

cd /sys/class/scsi_host/host?/

in there is a link_power_management_policy into which (as root) "min_power" and "max_performace" can be written. The latter should be there by default. So one would twiddle from max_performance to min_power and back. Then do some reading operations involving the disk. In my case I seem to get

ata3: exception Emask 0x10 SAct 0x0 SErr 0x50000 action 0xe frozen
[46446.498522] ata3: irq_stat 0x00400000, PHY RDY changed
[46446.498538] ata3: SError: { PHYRdyChg CommWake }
[46446.498559] ata3: hard resetting link
[46447.220211] ata3: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[46447.222302] ata3.00: ACPI cmd ef/10:03:00:00:00:a0 (SET FEATURES) filtered out
[46447.242143] ata3.00: ACPI cmd ef/10:03:00:00:00:a0 (SET FEATURES) filtered out
[46447.242603] ata3.00: configured for UDMA/133
[46447.242623] ata3: EH complete

once in dmesg and without any visible effects on the reading operations. In the bad case there would be hard errors (involving timeouts), repeating and with errors reported to the reading operation.