bonjoiur
Sibsib a trouvé un script que j'ai testé sur sme
https://github.com/mlogic/suspend-usb-device#!/bin/bash
## set -x
#
#
#  suspend-usb-device: an easy-to-use script to properly put an USB
#  device into suspend mode that can then be unplugged safely
#
#  Copyright (C) 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
#  Yan Li <elliot.li.tech@gmail.com>
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
#  To reach the auther, please write an email to the address as stated
#  above.
#  ACKNOWLEDGEMENTS:
#      Christian Schmitt <chris@ilovelinux.de> for firewire supporting
#      David <d.tonhofer@m-plify.com> for improving parent device
#      search and verbose output message
usage()
{
    cat<<EOF
suspend-usb-device  Copyright (C) 2009-2016, Yan Li <elliot.li.tech@gmail.com>
This script is designed to properly put an USB device into suspend
mode that can then be unplugged safely. It sends a SYNCHRONIZE CACHE
command followed by a START-STOP command (if the device supports it),
unbinds the device from the driver and then suspends the USB
port. After that you can disconnect your USB device safely.
usage:
$0 [options] dev
sample:
$0 /dev/sde
options:
  -l     show the device and USB bus ID only
  -h     print this usage
  -v     verbose
This program comes with ABSOLUTELY NO WARRANTY.  This is free
software, and you are welcome to redistribute it under certain
conditions; for details please read the licese at the beginning of the
source code file.
EOF
}
set -e -u
SHOW_DEVICE_ONLY=0
VERBOSE=0
while getopts "vlh" opt; do
    case "$opt" in
        h)
            usage
            exit 2
            ;;
        l)
            SHOW_DEVICE_ONLY=1
            ;;
        v)
            VERBOSE=1
            ;;
        ?)
            echo
            usage
            exit 2
            ;;
    esac
done
DEV_NAME=${!OPTIND:-}
if [ -z ${DEV_NAME} ]; then
    usage
    exit 2
fi
# mount checking
if mount | grep "^${DEV_NAME}[[:digit:]]* "; then
    1>&2 echo
    1>&2 echo "the above disk or partition is still mounted, can't suspend device"
    1>&2 echo "unmount it first using umount"
    exit 1
fi
# looking for the parent of the device with type "usb-storage:usb", it
# is the grand-parent device of the SCSI host, and it's devpath is
# like
# /devices/pci0000:00/0000:00:1d.7/usb5/5-8 (or /fw5/fw5-8 for firewire devices)
# without an USB hub, the device path looks like:
# /devices/pci0000:00/0000:00:1d.7/usb2/2-1/2-1:1.0/host5/target5:0:0/5:0:0:0
# here the grand-parent of host5 is 2-1
# when there's a USB HUB, the device path is like:
# /devices/pci0000:00/0000:00:1d.0/usb5/5-2/5-2.2/5-2.2:1.0/host4/target4:0:0/4:0:0:0
# and the grand-parent of host4 is 5-2.2
DEVICE=$(udevadm info --query=path --name=${DEV_NAME} --attribute-walk | \
    egrep "looking at parent device" | head -1 | \
    sed -e "s/.*looking at parent device '\(\/devices\/.*\)\/.*\/host.*/\1/g")
if [ -z $DEVICE ]; then
    1>&2 echo "cannot find appropriate parent USB/Firewire device, "
    1>&2 echo "perhaps ${DEV_NAME} is not an USB/Firewire device?"
    exit 1
fi
# the trailing basename of ${DEVICE} is DEV_BUS_ID ("5-8" in the
# sample above)
DEV_BUS_ID=${DEVICE##*/}
[[ $VERBOSE == 1 ]] && echo "Found device $DEVICE associated to $DEV_NAME; USB bus id is $DEV_BUS_ID"
if [ ${SHOW_DEVICE_ONLY} -eq 1 ]; then
    echo Device: ${DEVICE}
    echo Bus ID: ${DEV_BUS_ID}
    exit 0
fi
# flush all buffers
sync
# root check
if [ `id -u` -ne 0 ]; then
    1>&2 echo error, must be run as root, exiting...
    exit 1
fi
# send SCSI sync command, some devices don't support this so we just
# ignore errors with "|| true"
#[[ $VERBOSE == 1 ]] && echo "Syncing device $DEV_NAME"
sdparm --command=sync "$DEV_NAME" >/dev/null || true
# send SCSI stop command
#[[ $VERBOSE == 1 ]] && echo "Stopping device $DEV_NAME"
sdparm --command=stop "$DEV_NAME" >/dev/null
# unbind it; if this yields "no such device", we are trying to unbind the wrong device
[[ $VERBOSE == 1 ]] && echo "Unbinding device $DEV_BUS_ID"
if [[ "${DEV_BUS_ID}" == fw* ]]
then
    echo -n "${DEV_BUS_ID}" > /sys/bus/firewire/drivers/sbp2/unbind
else
    echo -n "${DEV_BUS_ID}" > /sys/bus/usb/drivers/usb/unbind
    # suspend it if it's an USB device (we have no way to suspend a
    # firewire device yet)
    # USB power level control is deprecated since 2.6.32. If both power/control
    # and power/level files exist, we are using a new kernel that doesn't support
    # force suspending a USB device. If only the power/level file exists, we
    # will try to suspend the device.
    [[ $VERBOSE == 1 ]] && echo "Checking whether $DEVICE can be suspended"
    POWER_LEVEL_FILE=/sys${DEVICE}/power/level
    POWER_CONTROL_FILE=/sys${DEVICE}/power/control
    if [ ! -f "$POWER_CONTROL_FILE" -a ! -f "$POWER_LEVEL_FILE" ]; then
        1>&2 cat<<EOF
It's safe to remove the USB device now but better can be done. The
power level control file $POWER_LEVEL_FILE
doesn't exist on the system so I have no way to put the USB device
into suspend mode, perhaps you don't have CONFIG_USB_SUSPEND enabled
in your running kernel.
Read
http://elliotli.blogspot.com/2009/01/safely-remove-usb-hard-drive-in-linux.html
for an detailed explanation.
EOF
        exit 3
    elif [ ! -f "$POWER_CONTROL_FILE" ]; then
        # Only the power/level file exists, try to suspend the device
        [[ $VERBOSE == 1 ]] && echo "Suspending $DEVICE by writing to $POWER_LEVEL_FILE"
        echo 'suspend' > "$POWER_LEVEL_FILE"
    fi
    # Do nothing if power/control or both files exist.
fi
J'ai installé sdparm
# yum install sdparm
=> 
sdparm                                               x86_64                                               1.04-1.1.el6                                                 base                                                99 k
J'ai mis un dock  usb avec mon serveur sme.
J'ai mis un disque de 2to pour mes sauvegardes
l# lsusb
...
Bus 001 Device 011: ID 152d:2352 JMicron Technology Corp. / JMicron USA Technology Corp. ATA/ATAPI Bridge
...
# ls -al /dev/sd*
brw-rw---- 1 root disk 8,  0 22 janv. 21:23 /dev/sda
brw-rw---- 1 root disk 8,  1 22 janv. 21:23 /dev/sda1
brw-rw---- 1 root disk 8,  2 22 janv. 21:23 /dev/sda2
brw-rw---- 1 root disk 8,  3 22 janv. 21:23 /dev/sda3
brw------- 1 root root 8, 16 23 janv. 22:50 /dev/sdb
brw------- 1 root root 8, 17 23 janv. 22:50 /dev/sdb1
brw------- 1 root root 8, 18 23 janv. 22:50 /dev/sdb2
Je recheche le bus
# ./suspend-usb-device.sh  -vl /dev/sdb
Found device /devices/pci0000:00/0000:00:12.2/usb1/1-2/1-2.5/1-2.5.5 associated to /dev/sdb; USB bus id is 1-2.5.5
Device: /devices/pci0000:00/0000:00:12.2/usb1/1-2/1-2.5/1-2.5.5
Bus ID: 1-2.5.5
A la fin du traitement de la sauvegarde, je mets le disque en standby.
# ./suspend-usb-device.sh  -v /dev/sdb
Found device /devices/pci0000:00/0000:00:12.2/usb1/1-2/1-2.5/1-2.5.5 associated to /dev/sdb; USB bus id is 1-2.5.5
Unbinding device 1-2.5.5
Checking whether /devices/pci0000:00/0000:00:12.2/usb1/1-2/1-2.5/1-2.5.5 can be suspended
# ls -al /dev/sd*
brw-rw---- 1 root disk 8, 0 22 janv. 21:23 /dev/sda
brw-rw---- 1 root disk 8, 1 22 janv. 21:23 /dev/sda1
brw-rw---- 1 root disk 8, 2 22 janv. 21:23 /dev/sda2
brw-rw---- 1 root disk 8, 3 22 janv. 21:23 /dev/sda3
Plus de disque /dev/sdb
Le disque c'est arrêté de tourner et donc ne chauffe plus.
Je remets le disque en fonction
# echo -n "1-2.5.5" >/sys/bus/usb/drivers/usb/bind
A retester et à paufiner
Anne