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I know the linux command

echo "- - -" > /sys/class/scsi_host/host0/scan

is used to rescan scsi host. But what does "- - -" mean in the command?

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It means that you are echoing a wildcard value of "channel target and lun", and the operating system will rescan the device path. As said bellow, there are plenty of Red Hat docs about scsi configuration :) – nwildner Mar 22 '13 at 11:00
up vote 11 down vote accepted

The three values stand for channel, SCSI target ID, and LUN. The dashes act as wildcards meaning "rescan everything"

A quick google search turns up this RHEL doc (and dozens of other answers)

This is the same command described in Section 7, “Adding a Storage Device or Path” to add a storage device or path. In this case, however, the channel number, SCSI target ID, and LUN values are replaced by wildcards. Any combination of identifiers and wildcards is allowed, allowing you to make the command as specific or broad as needed. This procedure will add LUNs, but not remove them.

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