Linux Storage - mppBusRescan commands

category: solutionz · date: 2010-09-30 · updated: 2026-10-03 · author: LALA

Linux Storage Solution · Config document · referenced from RDAC installation and operation

noteThe outputs of mppBusRescan -s, -d, -u and -c show mptscsih adapters host0 to host5 and a virtual host host6 with disks sdo and sdp. That is not mppsrv01, which has two qla2xxx HBAs and the virtual adapter host2; those four outputs were kept from another machine or from documentation, and the notes do not say which. Only the plain mppBusRescan output is from this host.

mppBusRescan, also reachable as hot_add (/usr/sbin/hot_add is a link to /usr/sbin/mppBusRescan), is the RDAC (MPP) driver's way of finding a new array or LUN on the SAN without a reboot, of removing devices that were unmapped or disconnected, of picking up a remapped LUN and of refreshing a LUN whose size has changed. It scans the physical HBAs first, then has the driver build the virtual LUNs (mppUtil -s busscan), then scans the virtual adapter.

Item	Value
Command	`/usr/sbin/mppBusRescan`, link `/usr/sbin/hot_add`
Run as	`root` on `mppsrv01` (the plain `mppBusRescan` example); the `-s`, `-d`, `-u`, `-c` examples are from another host, see the note
Host	Red Hat Enterprise Linux AS 4, kernel `2.6.9-89.0.9.ELsmp`, HBAs `host0` and `host1` (`qla2xxx`), virtual MPP adapter `host2`
Found	the standby array `DS5300-SITEB`: targets 2 and 3 on both HBAs, LUNs 1 and 2, as `/dev/sdc` and `/dev/sdd` on `host2`
Driver version	RDAC `09.03.0B05.0331`

The commands

The usage list as the notes keep it. Each task has a long and a short option, and the first two tasks can be given to hot_add or to mppBusRescan alike; the notes list the alternatives with "or" between them, and here they stand as consecutive lines. None of these lines has output in the notes:

bash

$ mppBusRescan
$ mppBusRescan -s
$ mppBusRescan --scan
$ hot_add
$ hot_add -s
$ hot_add --scan
$ hot_add -d
$ hot_add --delete
$ mppBusRescan -d
$ mppBusRescan --delete
$ mppBusRescan -u
$ mppBusRescan --update
$ mppBusRescan -c
$ mppBusRescan --capacity

Lines	Task, as the notes word it
`mppBusRescan`, `-s`, `--scan`, or `hot_add` with the same options	find (scan) a new disk array on the physical bus (the SAN); the plain command scans too
`hot_add -d`, `--delete`, or `mppBusRescan` with the same options	remove (delete) an unmapped or disconnected device
`mppBusRescan -u`, `--update`	check whether a device or LUN has changed; if so, update RDAC with the newly remapped device or LUN
`mppBusRescan -c`, `--capacity`	check whether the capacity of a device or LUN has changed; if so, update its capacity

The examples with output

Finding the new disk array on mppsrv01. The two QLogic hosts are scanned first, the driver is told to scan (mppUtil -s busscan), and the virtual host host2 is scanned last and gives the new LUNs their disk names:

bash

$ mppBusRescan

output 14 lines

scan qla2 HBA host /sys/class/scsi_host/host1...
        found 1:0:2:1
        found 1:0:2:2
        found 1:0:3:1
        found 1:0:3:2
scan qla2 HBA host /sys/class/scsi_host/host0...
        found 0:0:2:1
        found 0:0:2:2
        found 0:0:3:1
        found 0:0:3:2
run /usr/sbin/mppUtil -s busscan...
scan mpp virtual host /sys/class/scsi_host/host2...
        found 2:0:1:1->/dev/sdc
        found 2:0:1:2->/dev/sdd

The explicit scan, on the other machine (see the note):

bash

$ mppBusRescan -s

output 24 lines

Starting new devices re-scan...
scan mptscsih HBA host /sys/class/scsi_host/host5...
       no new device found
scan mptscsih HBA host /sys/class/scsi_host/host4...
       no new device found
scan mptscsih HBA host /sys/class/scsi_host/host3...
       no new device found
scan mptscsih HBA host /sys/class/scsi_host/host2...
       found 2:0:0:7
       found 2:0:0:9
       found 2:0:1:7
       found 2:0:1:9
       found 2:0:2:7
       found 2:0:2:9
       found 2:0:3:7
       found 2:0:3:9
scan mptscsih HBA host /sys/class/scsi_host/host1...
       no new device found
scan mptscsih HBA host /sys/class/scsi_host/host0...
       no new device found
run /usr/sbin/mppUtil -s busscan...
scan mpp virtual host /sys/class/scsi_host/host6...
       found 6:0:0:7->/dev/sdo
       found 6:0:0:9->/dev/sdp

Removing unmapped or disconnected devices, same machine:

bash

$ mppBusRescan -d

output 3 lines

Searching for unmapped or disconnected MPP devices.
Found 6:0:0:7/sdo as unmapped/disconnected device. Device removed.
Found 6:0:0:9/sdp as unmapped/disconnected device. Device removed.

Checking for a remapped device or LUN and updating RDAC with it:

bash

$ mppBusRescan -u

output 3 lines

Searching for remapped MPP devices.
Found 6:0:0:7/sdo as remapped device. Device updated.
Found 6:0:0:9/sdp as remapped device. Device updated.

Checking for a changed capacity and updating it:

bash

$ mppBusRescan -c

output 3 lines

Searching for MPP device with size modified
Found 6:0:0:7/sdo with size modified. Device size updated.
Found 6:0:0:9/sdp with size modified. Device size updated.

Reading the outputs

Line	Reading
`scan qla2 HBA host /sys/class/scsi_host/host1...`	the tool walks the SCSI hosts of the low-level driver and asks each for new devices; `host1` came first here
`found 1:0:2:1` … `found 0:0:3:2`	eight new physical devices, `host:channel:target:lun`: on each HBA two new targets (2 and 3, the two controllers of `DS5300-SITEB`) with LUNs 1 and 2. These are exactly the eight devices removed in Hot removal of a LUN
`run /usr/sbin/mppUtil -s busscan...`	the driver is told to look at the new physical devices and build the virtual LUNs
`scan mpp virtual host /sys/class/scsi_host/host2...`	the virtual adapter is scanned last
`found 2:0:1:1->/dev/sdc`, `found 2:0:1:2->/dev/sdd`	the two virtual LUNs of the new array (target 1 on the virtual adapter, which is the `H2C0T1` of its `.wwn` file) and the disk names they got; `lsvdev` shows the same mapping, see mppUpdate and lsvdev
`scan mptscsih HBA host …host5`, `found 6:0:0:7->/dev/sdo`	the other machine: six hosts of the `mptscsih` driver (as I know it, the LSI Fusion-MPT driver, not the QLogic one of `mppsrv01`), the new devices as LUNs 7 and 9 on four targets of `host2`, the virtual adapter as `host6`. The shape of the output is the same, and presumably that is why the notes kept it

In the plain example the two LUNs of the standby array became /dev/sdc and /dev/sdd next to /dev/sda and /dev/sdb of the main array. Because the standby array is a mirror of the main one, this is the "two arrays" state that problem 1 in RDAC problems and LUN removal removes again.

Checked against sg3_utils 1.49 and Red Hat Enterprise Linux 10

As built	Today
`hot_add` as a link to `mppBusRescan`	Confirmed by the package readme: "hot_add is a symbolic link to mppBusRescan". The same readme says "the Linux RDAC driver doesn't support LUN deletion", which sits oddly next to the `-d` option that removes unmapped or disconnected devices; I read it as the driver not handling a LUN that disappears under it, which is what problem 2 in RDAC problems and LUN removal works around
the driver's own rescan of the HBAs and the virtual adapter	Without RDAC the generic tools do it: `rescan-scsi-bus.sh` from sg3_utils (script version 20260526 in the current tree; sg3_utils release 1.49), which still writes to `/sys/class/scsi_host/hostN/scan`, is what SUSE documents; `scsi-rescan` is a Red Hat and Fedora symlink to it. Red Hat's current guide shows only `echo 1 > /sys/block/sdX/device/rescan` after a LUN resize and `issue_lip`
`mppBusRescan -c` for a changed capacity, `-d` for removal	`echo 1 > /sys/block/sdX/device/rescan` and `echo 1 > /sys/block/sdX/device/delete` in the Red Hat Enterprise Linux 9 and 10 guides
RDAC itself	Discontinued with SANtricity OS 11.25; the arrays' line continues as NetApp E-Series with DM-Multipath and `scsi_dh_rdac`