scan for luns

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Hello guys,

thanks for helping me with this. If you have your SAN connect to RHEL by fiber channel , how do you scan for luns?

I have worked with iscsi, I can't find any documents from red hat documenting how to scan for luns connected by fiber channel.

Thanks guys

Arrey

aa
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Responses

F. Active Contributor 273 points
12 June 2014 6:38 PM

Hi Ashu,
Make the operating system aware of the new storage device, or path to an existing device. The recommended command to use is:

echo "c t l" > /sys/class/scsi_host/hosth/scan

In the previous command, h is the HBA number, c is the channel on the HBA, t is the SCSI target ID, and l is the LUN.

It should look like something like this.

echo "0 2 56" > /sys/class/scsi_host/host5/scan

Refer to this article.

https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/Online_Storage_Reconfiguration_Guide/adding_storage-device-or-path.html

james.radtke@siriusxm.com's picture Guru 6863 points
12 June 2014 7:06 PM

The advice above is solid.

I generally will install sg3_utils and run rescan-scsi-bus.sh

ls -l /dev/sd* > /var/tmp/sd-0.out
multipath -ll -v2 > /var/tmp/multipath-ll-v2-0.out
yum -y install sg3_utils
rescan-scsi-bus.sh
ls -lart /dev/sd* 
ls -lart /dev/mapper

Then to review the differences...

ls -l /dev/sd* > /var/tmp/sd-1.out
multipath -ll -v2 > /var/tmp/multipath-ll-v2-1.out
sdiff /var/tmp/sd-0.out /var/tmp/sd-1.out
sdiff /var/tmp/multipath-ll-v2-0.out /var/tmp/multipath-ll-v2-1.out
aa Pro 639 points
12 June 2014 7:20 PM

Thanks guys for the info. Very helpful . I think rescan-scsi-bus.sh is the best way to go. In solaris, devfsadm is all that is needed. Thanks again guys

F. Active Contributor 273 points
12 June 2014 8:13 PM

Thanks to James, very useful info.

james.radtke@siriusxm.com's picture Guru 6863 points
12 June 2014 8:17 PM

My pleasure - I think rescan-scsi-bus.sh is the closest you will get to replacing "devfsadm -Cv" - depending on what I am doing, I may also compare /proc/diskstats or some other output to make sure that the devices were discovered.

VT Community Member 60 points
26 January 2016 7:05 AM

While convenient, rescan-scsi-bus.sh has known issues that you need to be aware of. See https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/logical-unit-add-remove.html. There are no issues with the 'echo' command provided above by Farrukh.

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