Disks

Rescan SCSI or FC devices

When you are playing with SCSI devices (like Fibre Channel, SAS, ..) you sometimes need to rescan the SCSI bus to add devices or to tell the kernel a device is gone. Well, this is the way to do it in CentOS with versions that have a 2.6 kernel. This means CentOS 5 and CentOS 4 (starting from update 3).

Find what's the host number for the HBA:

ls /sys/class/fc_host/

(You'll have something like host1 or host2, I'll refer to them as host$NUMBER from now on)

Ask the HBA to issue a LIP signal to rescan the FC bus:

echo 1 >/sys/class/fc_host/host$NUMBER/issue_lip

Wait around 15 seconds for the LIP command to have effect

Ask Linux to rescan the SCSI devices on that HBA:

echo - - - >/sys/class/scsi_host/host$NUMBER/scan

The wildcards "- - -" mean to look at every channel, every target, every lun.

Rescan for after disk was extended

echo "1" > /sys/block/sda/device/rescan

How to use a new partition in RHEL6 without reboot?

partx -a /dev/sd

Use cases:

existing disk extending on RH6

echo 1 > /sys/block/sda/device/rescan
fdisk -l
fdisk /dev/sda
partx /dev/sda
partx -a /dev/sda
pvcreate /dev/sda4
vgextend VG01 /dev/sda4
lvextend -L +14G /dev/VG01/logs 
lvextend -L +14G /dev/VG01/var 
resize2fs /dev/VG01/logs
resize2fs /dev/VG01/var
df -h