What is lun in linux

🐧 Как сканировать / обнаруживать новые LUN и SCSI-диски на Linux

Когда система Linux подключена к SAN (Storage Area Network), вам необходимо повторно просканировать службу iSCSI, чтобы обнаружить новые LUN.

Для этого вы должны предоставить группе хранения данных номер WWN хоста Linux и требуемый размер LUN.

После того, как группа хранения сопоставит LUN с заданным хостом Linux, они предоставят вам новые сведения о LUN.

LUN в терминах хранения называется последовательным шестнадцатеричным номером LUN.

Вам необходимо просканировать хост SCSI, чтобы найти новые LUN, назначенные группой хранения.

Это можно сделать двумя способами: сканировать каждое хост-устройство scsi или запустить скрипт rescan-scsi-bus.sh для обнаружения новых дисков.

После сканирования их можно будет найти в каталоге «/dev/disk/by-id».

Кроме того, вы можете найти их с помощью команды Multipath, если они уже настроены с Multipath.

Multipath в основном настраивается на сервере базы данных Oracle для повышения производительности.

Метод 1: Как найти новые LUN и SCSI-диски в Linux с помощью файла класса «/ sys»

Файловая система sysfs – это псевдофайловая система, которая предоставляет интерфейс для структур данных ядра.

Файлы в sysfs предоставляют информацию об устройствах, модулях ядра, файловых системах и других компонентах ядра.

Файловая система sysfs обычно монтируется в «/sys».

Обычно она устанавливается системой автоматически.

Вы можете использовать команду echo для сканирования каждого хост-устройства scsi, как показано ниже.

• c – Канал на HBA
• t – целевой идентификатор SCSI
• l – LUN ID
• n – номер HBA

Выполните приведенную ниже команду, чтобы найти все номера хост-шины в вашей системе.

Как только вы получите номер хост-шины, выполните следующую команду, чтобы обнаружить новые диски.

Кроме того, их можно просканировать с помощью «цикла for» с помощью одной команды.

Вы можете проверить их с помощью команды ls, как упоминалось в начале статьи.

Метод 2: Как просканировать новые LUN и SCSI-диски в Linux с помощью скрипта

Убедитесь, что вы уже установили пакет «sg3_utils», чтобы использовать этот сценарий. В противном случае выполните следующую команду, чтобы установить его.

Для систем RHEL/CentOS 6/7 используйте команду yum для установки sg3_utils.

Для систем RHEL / CentOS 8 и Fedora используйте команду dnf для установки sg3_utils.

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How to Check LUN or SAN Disk in Linux

When you are working in a storage environment, it is often desirable to add, remove or re-size storage devices. Once storage is allocated we need to scan and verify allocated storage SAN disk.

In this article, I will show commands to check/identify the attached LUN information in a Linux system.

What is a LUN

A LUN is a Logical Unit Number. It can be used to refer to an entire physical disk, or a subset of a larger physical disk or disk volume. The physical disk or disk volume could be an entire single disk drive, a partition (subset) of a single disk drive, or disk volume from a RAID controller comprising multiple disk drives aggregated together for larger capacity and redundancy.

1) Check attached LUN or SAN disk in Linux

To check the attached LUN from a storage device in Linux, we can use the /proc/scsi/scsi file content but it will give you some information and you can not be able to distinguish physical attached drive to LUN. Display the content as below as below

Normally Luns would be showing as Host: scsi3 Channel: 00 Id: 00 Lun: 00

Below is another example of the same file where it’s using a different storage vendor.

You can use iscsiadm (only used when storage using iscsi target) command to get information about attached lun.

You can also check below path for lun information.

2) Using multipath command

Redhat default multipathing service is multipathd daemon. Below commands are from a server that has a multipathing enabled using multipathd daemon and from its output you can check OS identified Lun information.

Hope this article helped you to gather lun information on your Linux operating system. Please provide your comments and suggestion on the below section.

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How to Scan/Detect New LUNs on Linux

When you are running RedHat Enterprise Linux 5, 6, and 7 series system with DM-Multipath and the software iSCSI initiator, you can discover new LUNs by rescanning the iSCSI service on the host.

Rescanning the service will display all the newly created LUNs that have been mapped to the host. In this tutorial I will show commands to scan and detect (outputs to check) new luns attached to the Centos/RHEL server.

To scan new FC LUNS and SCSI disks in Linux, you can use the echo script command for a manual scan that doesn’t require a system reboot. But, from Redhat Linux 5.4 onwards, Redhat introduced /usr/bin/rescan-scsi-bus.sh script to scan all the LUNs and update the SCSI layer to reflect new devices.

Check the number of attached disks

You use the below commands to identify existing LUNs and how to add newly mapped LUNs to Linux.

You can use the following command to have better output of all the disks

1) Using /sys class file

You can use the echo command to scan each scsi host device as below. Now to rescan the bus, use the following command

The three dash («- — -«) of the command act as wildcards meaning rescan everything. Remember that the three values normally stand for channel, SCSI target ID, and LUN.

• h is the HBA number
• c is the channel on the HBA
• t is the SCSI target ID
• l is the LUN.

If you don’t have the host bus number, you must list all the existing host bus number on your system with the command

Then you will scan every iscsi disk found and scan after every scanning if the new disk was detected. It means

It may look like very simple as we perform this operation but the system has much work to do in the background when you execute storage scanning commands.

Method to find Channel Routes

If we know the channel, target ID and LUN address, we can scan using that. Here, we have 4 HBA emulex cards 0, 1, 2 and 3.

Through card 0 and 2,

It has the same WWNN (World Wide Node Name) for all the 4 WWPN (World Wide Port Name).

We can do a depth research by filtering the WWPN (World Wide Port Name) to have more information

This indicates there are four Fibre Channel routes to this target.

So now, you can scan for LUNs as follows and addresss «8» is given by storage team.

The output of SCSI file is illustrated for your reference:

Another Method

If you don’t have the host bus number, you must list all the existing host bus number on your system with the command

On the output, host0 is the relevant field. As we have said earlier, we need to have the host bus number to determine what to scan

Then you will scan every iscsi disk found and scan after every scanning if the new disk was detected. It means

If you have too many hosts (from host0 to host20 for example), you can use the command below

or you can try (this one for Fibre Channel)

# for host in `ls /sys/class/fc_host/`; do
echo «1» >/sys/class/fc_host/$/issue_lip;
done

Can devices be rescanned in Linux OS without reloading the Linux driver?

There is a procedure which forces the driver to rescan the targets and to allow a new device which is to be added. This triggers the driver to initiate a LUN discovery process.

To force a rescan from the command line, type the following command:

# echo «scsi-qlascan» > /proc/scsi//

— = qla2100, qla2200, qla2300 (2.4 kernel drivers) or qla2xxx (2.6 kernel drivers)
— = the instance number of the HBA

After executing this command, force the SCSI mid layer to do its own scan and build the device table entry for the new device by typing the following command:

# echo «scsi add-single-device 0 1 2 3» >/proc/scsi/scsi

— «0 1 2 3» = your «Host Channel ID LUN»

The scanning must be done in the above-mentioned order; first the driver (qla2300/qla2200 driver, etc.) and then the Linux SCSI mid-layer (i.e. OS scan).

2) Scan lun with multipath/powermt

You can check current multipath setup using multipath or powermt command.

If EMC powerpath is installed, check the disk/multipath status as below:

Multipath daemon will automatically add attached devices if it’s configured properly. For powermt, we need to run below command manually.

3) Using Script

You can rescan using the SCSI rescan script which will detect new luns and add it to your server automatically. You can find this script in sg3_utils package.

Conclusion

For storage (Netapp,equallogic) that use iscsi target, command iscsiadm -m session —rescan could be used to rescan when new lun added to the target. I would recommend always to use vendor-specific script or tools to scan Luns.

I hope you have enjoyed reading and let us know if you found any other method to scan storage disk devices.

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What is the difference between LVM and LUN

Both seem to be a virtualization layer on top of physical disks. I’m having a hard-time understanding each of them and the difference between them.

4 Answers 4

Different layers of abstraction.

If you’ve got a large storage array, you probably don’t want one server to use the whole thing, so you divide it into logical units (LUN is actually Logical Unit Number, but hey, it helps me remember). So you’ve got your storage sliced into usable chunks, and now you present it to the server. In a simple example, suppose it shows up as /dev/sdb. No partitions on it, it’s just a disk, so far as the server cares.

Why throw LVM on top of it? For me, it’s because of growth. If I fill up that disk, I want to be able to add more space to it. LVM makes it easier and (in my mind) less risky, because I can resize that LUN on the storage array (or even create another LUN and present that to the server) and using LVM, I can grow the «virtual» disk without rebooting.

LVM is a piece of software used to «carve» up a disk, usually a locally attached disk, into smaller sections.

LVM is a method of allocating hard drive space into logical volumes that can be easily resized instead of partitions.

A LUN is a construct, usually on a storage array, with which you present a «slice» of a disk array/volume to a host, where it appears as a physically attached local disk via some connection, usually SAN (iSCSI/FC).

For example, if you presented a LUN to a host, you could then use LVM to further customize the layout of what the system thought was a local disk.

A LUN is a Logical Unit Number. It can be used to refer to an entire physical disk, or a subset of a larger physical disk or disk volume. The physical disk or disk volume could be an entire single disk drive, a partition (subset) of a single disk drive, or disk volume from a RAID controller comprising multiple disk drives aggregated together for larger capacity and redundancy. LUNs represent a logical abstraction or, if you prefer, virtualization layer between the physical disk device/volume and the applications.

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How do you present a LUN in Linux?

How do I find LUNs in Linux?

How to Scan/Detect New LUNs on Linux

1. 1) Using /sys class file. You can use the echo command to scan each scsi host device as below. …
2. 2) Scan lun with multipath/powermt. You can check current multipath setup using multipath or powermt command. …
3. 3) Using Script. …
4. Conclusion.

What is Lun in Linux?

In computer storage, a logical unit number, or LUN, is a number used to identify a logical unit, which is a device addressed by the SCSI protocol or by Storage Area Network protocols that encapsulate SCSI, such as Fibre Channel or iSCSI.

How do I find my storage path in Linux?

1. How much space do I have free on my Linux drive? …
2. You can check your disk space simply by opening a terminal window and entering the following: df. …
3. You can display disk usage in a more human-readable format by adding the –h option: df –h. …
4. The df command can be used to display a specific file system: df –h /dev/sda2.

How do I find the WWN number of a LUN in Linux?

Here is a solution to find WWN number of HBA and scan the FC Luns.

1. Identify the number of HBA adapters.
2. To get the WWNN (World Wide Node Number) of HBA or FC card in Linux.
3. To get the WWPN (World Wide Port Number) of HBA or FC card in Linux.
4. Scan the newly added or rescan the existing LUNs in Linux.

How do I rescan a device in Linux?

When adding a new disk to your Linux system you need to rescan SCSI host.

1. You can do this with the following command: echo “- – -” > /sys/class/scsi_host/hostX/scan.
2. .. …
3. The easiest way i’ve found is to rescan the specific device with the following command: echo “1” > /sys/class/block/sdX/device/rescan.
4. ..

How do I scan a new FN Lun in Linux?

Scan new FC LUNS and SCSI disks in Linux

1. Identify the existing disks fdisk -l 2>/dev/null | egrep ‘^Disk’ | egrep -v ‘dm-|type|identifier’
2. Identify the number of HBA adapters systool -c fc_host -v or ls /sys/class/fc_host host0. …
3. Use the below command to scan the LUNs echo “1” > /sys/class/fc_host/host0/issue_lip echo “- – -” > /sys/class/scsi_host/host0/scan.

How do I configure Lun?

Set up the Linux host to use the LUN

1. Find the LUN ID: In Unisphere, select Storage > Block > LUNs. On the LUN, select Edit. …
2. On the host, partition the LUN.
3. Create a file system on the partition.
4. Create a mount directory for the file system.
5. Mount the file system.

What is Lun in Unix?

In simple terms, a logical unit number (LUN) is a slice or portion of a configured set of disks that is presentable to a host and mounted as a volume within the OS.

How do you add a LUN?

1. Navigate to the Virtual SAN cluster in the vSphere Web Client.
2. Click the Configure tab. Under Virtual SAN, click iSCSI Targets.
3. Select the LUNs tab in the Target Details section of the page.
4. Click the Add a new iSCSI LUN to the target ( ) icon. …
5. Enter the size of the LUN. …
6. Click OK.

How do I list all drives in Linux?

Listing Hard Drives in Linux

1. df. The df command in Linux is probably one of the most commonly used. …
2. fdisk. fdisk is another common option among sysops. …
3. lsblk. This one is a little more sophisticated but gets the job done as it lists all block devices. …
4. cfdisk. …
5. parted. …
6. sfdisk.

How do I find my device name Linux?

The procedure to find the computer name on Linux:

1. Open a command-line terminal app (select Applications > Accessories > Terminal), and then type:
2. hostname. hostnamectl. cat /proc/sys/kernel/hostname.
3. Press [Enter] key.

How do I find the WWN in Linux?

Answer: Use one of the following methods to view the HBA WWN address on Linux.

1. Method 1: /sys/class/scsi_host/host/device/fc_host:host/port_name File. …
2. Method 2: /proc/scsi// File. …
3. If you enjoyed this article, you might also like..

How do I find my WWN number in Linux?

1. Find WWN in Linux is easy using existing commands and installing few systools will help us in getting the FC HBA adapter WWN in Linux. …
2. We can use lspci command to find the FC HBA adapter details first. …
3. Method 1 # lspci |grep -i hba 0e:04.0 Fibre Channel: QLogic Corp.

How do I check my WWN?

There are several ways to detect the WWN of a Fibre Channel (FC) HBA and their details in Linux/Unix operating systems.
…
Purpose of wwn number

1. WWN – World Wide Name.
2. WWNN – World Wide Node Name.
3. WWPN – World Wide Port Name.
4. WWID – World Wide Identifier.
5. OUI – Organizationally Unique Identifier.

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