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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (How to Scan/Detect New LUNs and SCSI Disks on Linux)
+[#]: via: (https://www.2daygeek.com/scan-detect-luns-scsi-disks-on-redhat-centos-oracle-linux/)
+[#]: author: (Magesh Maruthamuthu https://www.2daygeek.com/author/magesh/)
+
+How to Scan/Detect New LUNs and SCSI Disks on Linux
+======
+
+When the Linux system has connected to the SAN (Storage Area Network) you need to rescan the iSCSI service to discover new LUNs.
+
+To do so, you must provide the WWN number of the Linux host and required LUN size to the storage team.
+
+The following article will help you [**find the WWN number of a Linux host**][1].
+
+Once the storage team has mapped the LUNs with the given Linux host, they will provide you with the new LUN details.
+
+LUN in storage terms is referred to as serial-hex of LUN.
+
+You need to scan the SCSI host to find new LUNs assigned by the storage team.
+
+This can be done in two ways, scan each scsi host device or run the “rescan-scsi-bus.sh” script to detect new disks.
+
+After scanning they can be found under the “/dev/disk/by-id” directory.
+
+```
+# ll /dev/disk/by-id
+
+total 0
+lrwxrwxrwx 1 root root 10 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684b -> ../../sdah
+lrwxrwxrwx 1 root root 9 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684c -> ../../sdw
+.
+.
+lrwxrwxrwx 1 root root 10 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684d -> ../../sdjk
+lrwxrwxrwx 1 root root 10 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684e -> ../../sdaa
+lrwxrwxrwx 1 root root 9 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684f -> ../../sdh
+```
+
+Also, you can find them using the Multipath command if you already have them configured with Multipath.
+
+Multipath is mostly configured into the Oracle database server for better performance.
+
+```
+# multipath -ll
+
+60a98000486e542d4f5a2f47694d684b dm-37 NETAPP,LUN C-Mode
+size=512G features='3 queue_if_no_path pg_init_retries 50' hwhandler='1 alua' wp=rw
+|-+- policy='round-robin 0' prio=50 status=active
+| |- 1:0:4:18 sdoe 128:416 active ready running
+| |- 0:0:4:18 sdpq 131:256 active ready running
+| |- 0:0:5:18 sdsr 135:496 active ready running
+| `- 1:0:5:18 sdsq 135:480 active ready running
+`-+- policy='round-robin 0' prio=10 status=enabled
+  |- 1:0:1:18 sdfw 131:32 active ready running
+  |- 1:0:0:18 sdci 69:96 active ready running
+  |- 0:0:1:18 sdbz 68:208 active ready running
+  |- 0:0:0:18 sds 65:32 active ready running
+  |- 1:0:3:18 sdmd 69:336 active ready running
+  |- 1:0:2:18 sdjj 8:464 active ready running
+  |- 0:0:3:34 sdjt 65:368 active ready running
+  `- 0:0:2:34 sdgi 131:224 active ready running
+```
+
+This procedure works on Red Hat 6.x, 7.x and 8.x (RHEL – Red Hat Enterprise Linux) based systems such as CentOS and Oracle Linux.
+
+### Method-1: How to Scan New LUNs and SCSI Disks on Linux Using the “/sys” Class File
+
+The sysfs filesystem is a pseudo-filesystem which provides an interface to kernel data structures.
+
+The files under sysfs provide information about devices, kernel modules, filesystems, and other kernel components.
+
+The sysfs filesystem is commonly mounted at “/sys”. Typically, it is mounted automatically by the system.
+
+You can use the echo command to scan each scsi host device as shown below.
+
+```
+# echo "- - -" > /sys/class/scsi_host/host[n]/scan
+```
+
+When you run the above command that rescan everything, the three dash (“- – -“) refers the wildcard option. These values would be as follow.
+
+```
+# echo "c t l" > /sys/class/scsi_host/host[n]/scan
+```
+
+where
+
+  * **c –** Channel on the HBA
+  * **t –** SCSI target ID
+  * **l –** LUN ID
+  * **n –** HBA number
+
+
+
+Run the below command to find all the host bus number on your system.
+
+```
+# ls /sys/class/scsi_host
+host0 host1 host2
+```
+
+Once you get the host bus number, run the following command to discover new disks.
+
+```
+# echo "- - -" > /sys/class/scsi_host/host0/scan
+# echo "- - -" > /sys/class/scsi_host/host1/scan
+# echo "- - -" > /sys/class/scsi_host/host2/scan
+```
+
+Also, it can be scanned using “for loop” with a single command.
+
+```
+# for host in ls /sys/class/scsi_host/;do echo "- - -" >/sys/class/scsi_host/${host}/scan; done
+```
+
+You can check them using the **[ls command][2]** as mentioned at the beginning of the article.
+
+```
+# ls /dev/disk/by-id | grep -i "serial-hex of LUN"
+```
+
+### Method-2: How to Scan New LUNs and SCSI Disks on Linux Using the rescan-scsi-bus.sh Script
+
+Make sure you have already installed the “sg3_utils” package to use this script. Otherwise, run the following command to install it.
+
+For **RHEL/CentOS 6/7** systems, use the **[yum command][3]** to install sg3_utils.
+
+```
+# yum install -y sg3_utils
+```
+
+For **RHEL/CentOS 8** and Fedora systems, use the **[dnf command][4]** to install sg3_utils.
+
+```
+# dnf install -y sg3_utils
+```
+
+Now you can rescan the LUNs using the rescan-scsi-bus.sh script.
+
+```
+# ./rescan-scsi-bus.sh
+```
+
+--------------------------------------------------------------------------------
+
+via: https://www.2daygeek.com/scan-detect-luns-scsi-disks-on-redhat-centos-oracle-linux/
+
+作者：[Magesh Maruthamuthu][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://www.2daygeek.com/author/magesh/
+[b]: https://github.com/lujun9972
+[1]: https://www.2daygeek.com/how-to-find-wwn-wwnn-wwpn-number-of-hba-card-in-linux/
+[2]: https://www.2daygeek.com/linux-unix-ls-command-display-directory-contents/
+[3]: https://www.2daygeek.com/linux-yum-command-examples-manage-packages-rhel-centos-systems/
+[4]: https://www.2daygeek.com/linux-dnf-command-examples-manage-packages-fedora-centos-rhel-systems/