2020-11-05 05:01:37 +08:00
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[#]: collector: (lujun9972)
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2020-11-06 08:52:50 +08:00
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[#]: translator: (geekpi)
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2020-11-05 05:01:37 +08:00
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (How to Scan/Detect New LUNs and SCSI Disks on Linux)
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[#]: via: (https://www.2daygeek.com/scan-detect-luns-scsi-disks-on-redhat-centos-oracle-linux/)
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[#]: author: (Magesh Maruthamuthu https://www.2daygeek.com/author/magesh/)
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How to Scan/Detect New LUNs and SCSI Disks on Linux
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======
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When the Linux system has connected to the SAN (Storage Area Network) you need to rescan the iSCSI service to discover new LUNs.
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To do so, you must provide the WWN number of the Linux host and required LUN size to the storage team.
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The following article will help you [**find the WWN number of a Linux host**][1].
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Once the storage team has mapped the LUNs with the given Linux host, they will provide you with the new LUN details.
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LUN in storage terms is referred to as serial-hex of LUN.
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You need to scan the SCSI host to find new LUNs assigned by the storage team.
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This can be done in two ways, scan each scsi host device or run the “rescan-scsi-bus.sh” script to detect new disks.
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After scanning they can be found under the “/dev/disk/by-id” directory.
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```
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# ll /dev/disk/by-id
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total 0
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lrwxrwxrwx 1 root root 10 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684b -> ../../sdah
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lrwxrwxrwx 1 root root 9 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684c -> ../../sdw
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.
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.
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lrwxrwxrwx 1 root root 10 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684d -> ../../sdjk
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lrwxrwxrwx 1 root root 10 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684e -> ../../sdaa
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lrwxrwxrwx 1 root root 9 Jul 9 17:52 scsi-60a98000486e542d4f5a2f47694d684f -> ../../sdh
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```
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Also, you can find them using the Multipath command if you already have them configured with Multipath.
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Multipath is mostly configured into the Oracle database server for better performance.
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```
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# multipath -ll
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60a98000486e542d4f5a2f47694d684b dm-37 NETAPP,LUN C-Mode
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size=512G features='3 queue_if_no_path pg_init_retries 50' hwhandler='1 alua' wp=rw
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|-+- policy='round-robin 0' prio=50 status=active
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| |- 1:0:4:18 sdoe 128:416 active ready running
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| |- 0:0:4:18 sdpq 131:256 active ready running
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| |- 0:0:5:18 sdsr 135:496 active ready running
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| `- 1:0:5:18 sdsq 135:480 active ready running
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`-+- policy='round-robin 0' prio=10 status=enabled
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|- 1:0:1:18 sdfw 131:32 active ready running
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|- 1:0:0:18 sdci 69:96 active ready running
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|- 0:0:1:18 sdbz 68:208 active ready running
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|- 0:0:0:18 sds 65:32 active ready running
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|- 1:0:3:18 sdmd 69:336 active ready running
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|- 1:0:2:18 sdjj 8:464 active ready running
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|- 0:0:3:34 sdjt 65:368 active ready running
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`- 0:0:2:34 sdgi 131:224 active ready running
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```
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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.
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### Method-1: How to Scan New LUNs and SCSI Disks on Linux Using the “/sys” Class File
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The sysfs filesystem is a pseudo-filesystem which provides an interface to kernel data structures.
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The files under sysfs provide information about devices, kernel modules, filesystems, and other kernel components.
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The sysfs filesystem is commonly mounted at “/sys”. Typically, it is mounted automatically by the system.
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You can use the echo command to scan each scsi host device as shown below.
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```
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# echo "- - -" > /sys/class/scsi_host/host[n]/scan
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```
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When you run the above command that rescan everything, the three dash (“- – -“) refers the wildcard option. These values would be as follow.
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```
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# echo "c t l" > /sys/class/scsi_host/host[n]/scan
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```
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where
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* **c –** Channel on the HBA
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* **t –** SCSI target ID
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* **l –** LUN ID
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* **n –** HBA number
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Run the below command to find all the host bus number on your system.
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```
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# ls /sys/class/scsi_host
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host0 host1 host2
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```
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Once you get the host bus number, run the following command to discover new disks.
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```
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# echo "- - -" > /sys/class/scsi_host/host0/scan
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# echo "- - -" > /sys/class/scsi_host/host1/scan
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# echo "- - -" > /sys/class/scsi_host/host2/scan
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```
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Also, it can be scanned using “for loop” with a single command.
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```
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# for host in ls /sys/class/scsi_host/;do echo "- - -" >/sys/class/scsi_host/${host}/scan; done
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```
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You can check them using the **[ls command][2]** as mentioned at the beginning of the article.
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```
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# ls /dev/disk/by-id | grep -i "serial-hex of LUN"
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```
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### Method-2: How to Scan New LUNs and SCSI Disks on Linux Using the rescan-scsi-bus.sh Script
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Make sure you have already installed the “sg3_utils” package to use this script. Otherwise, run the following command to install it.
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For **RHEL/CentOS 6/7** systems, use the **[yum command][3]** to install sg3_utils.
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```
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# yum install -y sg3_utils
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```
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For **RHEL/CentOS 8** and Fedora systems, use the **[dnf command][4]** to install sg3_utils.
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```
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# dnf install -y sg3_utils
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```
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Now you can rescan the LUNs using the rescan-scsi-bus.sh script.
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```
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# ./rescan-scsi-bus.sh
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```
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--------------------------------------------------------------------------------
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via: https://www.2daygeek.com/scan-detect-luns-scsi-disks-on-redhat-centos-oracle-linux/
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作者：[Magesh Maruthamuthu][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.2daygeek.com/author/magesh/
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[b]: https://github.com/lujun9972
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[1]: https://www.2daygeek.com/how-to-find-wwn-wwnn-wwpn-number-of-hba-card-in-linux/
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[2]: https://www.2daygeek.com/linux-unix-ls-command-display-directory-contents/
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[3]: https://www.2daygeek.com/linux-yum-command-examples-manage-packages-rhel-centos-systems/
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[4]: https://www.2daygeek.com/linux-dnf-command-examples-manage-packages-fedora-centos-rhel-systems/
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