CentOS 7.x adding or removing FC multipath disks without reboot

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For adding LVM on top of FC we do following:

1. Rescan fc devices using

   ls /sys/class/fc_host

   and then for each host

   echo "1" > /sys/class/fc_host/host0/issue_lip
   echo "- - -" > /sys/class/scsi_host/host0/scan

2. Check for device with lun ID in /dev/disk/by-id/
3. See if multipath is working (multipath -ll or service multipathd reload)
4. Create partition on multipath device (Fdisk or parted)
5. If partition is not appearing in /dev/mapper do partprobe
6. Create physical volution (pvcreate)
7. Add physical volume to volumegroup (vgcreate etc.)
8. Create Logical volume (lvmcreate, etc.)
9. Activate volume group (vgchange -a y <volgroup>)
10. Mount the device using /dev/mapper/<volgroup>-<logvol>

For removal we need to do the opposite which is at least:

1. Get device name from /dev/disk/by-id using LUN ID
2. Get multipath name from multipath -ll using device names
3. Get vg and lv names from "vgdisplay -v" using multipath name
4. Make sure that device is not mounted ( mount | grep <device>), otherwise umount
5. No open files (not possible after umount but just in cases), lsof | grep <device>
6. Device is not listed in activated volumegroups (vgdisplay -v), else deactivate using "vgchange -a n <volgroup-name>"
7. Once not listed in volumegroups remove multipath device using (multipath -f /dev/mapper/mpath<dev>
8. Now remove using "echo 1 > /sys/block/<device-name>/device/delete" for each device-name such as sda, sdb which need to be removed
9. If everything is fine following commands should finish within 1-2 seconds without any error display
   • fdisk -l
   • multipath -ll
   • vgscan
   • vgdisplay -v
   • pvscan
   • lvmdiskscan

Related article to get WWN of FC card at: CentOS 8.x Get FC HBA wwn for san zoning

Additionally refer:

• http://www.learnitguide.net/2016/02/scan-newly-added-fc-luns-and-scsi-disks.html
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/storage_administration_guide/removing_devices
• https://elkano.org/blog/removing-multipath-device/
• https://www.novell.com/coolsolutions/appnote/19386.html
• https://serverfault.com/questions/421776/removing-vg-and-lv-after-physical-drive-has-been-removed

Very good reference for Suse for above is available at https://www.suse.com/support/kb/doc/?id=7009660

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