Working with device in hot
Hot add, remove, rescan of SCSI devices on Linux
Finding informations about SCSI devices
The first problem when working with SCSI devices might be to map informations you got from /proc/scsi/scsi to the device names the kernel uses like /dev/sda and so on.
Or you can use lsscsi utlity. Here's an example:
# lsscsi
[0:0:0:0] disk ATA SEAGATE ST31000N SU0E /dev/sda
[0:0:1:0] disk ATA SEAGATE ST31000N SU0E /dev/sdb
...
[1:0:1:0] disk ATA SEAGATE ST31000N SU0E /dev/sdj
[1:0:2:0] disk ATA SEAGATE ST31000N SU0E /dev/sdk
[1:0:3:0] disk ATA HITACHI H7210CA3 A3CB /dev/sdl
[1:0:4:0] disk ATA HITACHI HUA7210S AC5A /dev/sdm
...
[5:0:7:0] disk ATA SEAGATE ST31000N SU0D /dev/sdav
[6:0:0:0] mediumx IBM TS3500 0104 /dev/sch0
[6:0:1:0] tape IBM ULT3580-TD5 0104 /dev/st0
[6:0:2:0] tape IBM ULT3580-TD5 0104 /dev/st1
You can find same info by checking /proc/scsi/scsi
# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: SEAGATE ST31000N Rev: SU0E
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi0 Channel: 00 Id: 01 Lun: 00
Vendor: ATA Model: SEAGATE ST31000N Rev: SU0E
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi0 Channel: 00 Id: 02 Lun: 00
Vendor: ATA Model: SEAGATE ST31000N Rev: SU0E
Type: Direct-Access ANSI SCSI revision: 05
...
In the example above
Host: scsi0 Channel: 00 Id: 01 Lun: 00
is the same device of [0:0:0:0] in the output of lsscsi
Where the output
h == hostadapter id (first one being 0)
c == SCSI channel on hostadapter (first one being 0)
t == ID
l == LUN (first one being 0)
Rescan of a SCSI bus
Surely reboot a server will let the scsi device get rescanned. But this is not the prefered way. The easiest way is to rescan the whole SCSI bus which will enable the Linux kernel to detect new devices!
To issue a SCSI bus rescan you must know on which bus you've added the device. If you don't know which bus and if there are mutliple buses on the system you can rescan each bus which will be somehow annoying but will not interrupt the system.
To initiate a SCSI bus rescan type
echo "- - -" > /sys/class/scsi_host/host<H>/scan
where H stands for the SCSI bus you want to scan.
# lsscsi
...
[1:0:0:7] disk IBM 1814 FAStT 1060 /dev/sdb
[1:0:0:8] disk IBM 1814 FAStT 1060 /dev/sdc
[1:0:0:10] disk IBM 1814 FAStT 1060 /dev/sde
# echo "- - -" > /sys/class/scsi_host/host1/scan
# lsscsi
...
[1:0:0:7] disk IBM 1814 FAStT 1060 /dev/sdb
[1:0:0:8] disk IBM 1814 FAStT 1060 /dev/sdc
[1:0:0:9] disk IBM 1814 FAStT 1060 /dev/sdd
[1:0:0:10] disk IBM 1814 FAStT 1060 /dev/sde
Well done, we got /dev/sdd back.
By the way this does not only work for disks but also for SCSI CD/DVD devices.
You can still use the old way, to get sdd back
echo "scsi add-single-device 1 0 0 9" > /proc/scsi/scsi
For more devices, you have to repeat the same for all devices
Deletion of a SCSI Device
There might be the situation where you must remove a SCSI device from the system.
Easy by using
echo 1 > /sys/class/scsi_device/h:c:t:l/device/delete
or
echo 1 > /sys/block/<dev>/device/delete
where <dev> is like sda or sdb etc..
Here's an example:
# echo 1 > /sys/block/sdau/device/delete
# lsscsi | grep sdau
#
Now you see the device sdau is gone.
In old way, this is what you would like to do
echo "scsi remove-single-device h c t l" > /proc/scsi/scsi
Add a SCSI Device back
Surely this can be done just rescan the SCSI bus that the disk seats inuse wildcard like below
echo "- - -" > /sys/class/scsi_host/host<h>/scan
You can also do this if you know the device SCSI location h:c:t:l
echo "c t l" > /sys/class/scsi_host/host<h>/scan
Old way
echo "scsi add-single-device a b c d" > /proc/scsi/scsi
Rescan of a SCSI Device
The problem of a SCSI bus rescan is, that it will only detect new devices. Can a existing or missing device be rescanned?
Sure, here is it
echo 1 > /sys/block/sdau/device/rescan
or
echo 1 > /sys/class/scsi_device/h:c:t:l/device/rescan
In SAN environment, there is a easier way to manage SAN scsi devices, see Sysfs fibre channel tools
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- Category: Storage