Vmware Linux Guest Add a New Hard Disk Without Rebooting Guest

Author: Last updated: January 6, 2018 51 comments

As a system admin, I need to use additional hard drives for to provide more storage space or to separate system data from user data. This procedure, adding physical block devices to virtualized guests, describes how to add a hard drive on the host to a virtualized guest using VMWare software running Linux as guest.

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It is possible to add or remove a SCSI device explicitly, or to re-scan an entire SCSI bus without rebooting a running Linux VM guest. This how to is tested under Vmware Server and Vmware Workstation v6.0 (but should work with older version too). All instructions are tested on RHEL, Fedora, CentOS and Ubuntu Linux guest / hosts operating systems.

Step # 1: Add a New Disk To Vm Guest

First, you need to add hard disk by visiting vmware hardware settings menu.
Click on VM > Settings

Fig.01: Vmware Virtual Machine Settings

Fig.01: Vmware Virtual Machine Settings

Alternatively you can press CTRL + D to bring settings dialog box.

Click on Add+ to add new hardware to guest:

Fig.02: VMWare adding a new hardware

Fig.02: VMWare adding a new hardware

Select hardware type Hard disk and click on Next

Fig.03 VMware Adding a new disk wizard

Fig.03 VMware Adding a new disk wizard

Select create a new virtual disk and click on Next

Fig.04: Vmware Wizard Disk

Fig.04: Vmware Wizard Disk

Set virtual disk type to SCSI and click on Next

Fig.05: Vmware Virtual Disk

Fig.05: Vmware Virtual Disk

Set maximum disk size as per your requirements and click on Next

Fig.06: Finalizing Disk Virtual Addition

Fig.06: Finalizing Disk Virtual Addition

Finally, set file location and click on Finish.

Step # 2: Rescan the SCSI Bus to Add a SCSI Device Without rebooting the VM

A rescan can be issued by typing the following command:
echo "- - -" > /sys/class/scsi_host/host#/scan
fdisk -l
tail -f /var/log/message
Sample outputs:

Linux Vmware Rescan New Scsi Disk Without Reboot

Fig.01:Linux Vmware Rescan New Scsi Disk Without Reboot

Replace host# with actual value such as host0. You can find scsi_host value using the following command:
# ls /sys/class/scsi_host
Output:

host0

Now type the following to send a rescan request:
echo "- - -" > /sys/class/scsi_host/host0/scan
fdisk -l
tail -f /var/log/message
Sample Outputs:

Jul 18 16:29:39 localhost kernel:   Vendor: VMware,   Model: VMware Virtual S  Rev: 1.0
Jul 18 16:29:39 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 02
Jul 18 16:29:39 localhost kernel:  target0:0:1: Beginning Domain Validation
Jul 18 16:29:39 localhost kernel:  target0:0:1: Domain Validation skipping write tests
Jul 18 16:29:39 localhost kernel:  target0:0:1: Ending Domain Validation
Jul 18 16:29:39 localhost kernel:  target0:0:1: FAST-40 WIDE SCSI 80.0 MB/s ST (25 ns, offset 127)
Jul 18 16:29:39 localhost kernel: SCSI device sdb: 2097152 512-byte hdwr sectors (1074 MB)
Jul 18 16:29:39 localhost kernel: sdb: Write Protect is off
Jul 18 16:29:39 localhost kernel: sdb: cache data unavailable
Jul 18 16:29:39 localhost kernel: sdb: assuming drive cache: write through
Jul 18 16:29:39 localhost kernel: SCSI device sdb: 2097152 512-byte hdwr sectors (1074 MB)
Jul 18 16:29:39 localhost kernel: sdb: Write Protect is off
Jul 18 16:29:39 localhost kernel: sdb: cache data unavailable
Jul 18 16:29:39 localhost kernel: sdb: assuming drive cache: write through
Jul 18 16:29:39 localhost kernel:  sdb: unknown partition table
Jul 18 16:29:39 localhost kernel: sd 0:0:1:0: Attached scsi disk sdb
Jul 18 16:29:39 localhost kernel: sd 0:0:1:0: Attached scsi generic sg1 type 0
Jul 18 16:29:39 localhost kernel:   Vendor: VMware,   Model: VMware Virtual S  Rev: 1.0
Jul 18 16:29:39 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 02
Jul 18 16:29:39 localhost kernel:  target0:0:2: Beginning Domain Validation
Jul 18 16:29:39 localhost kernel:  target0:0:2: Domain Validation skipping write tests
Jul 18 16:29:39 localhost kernel:  target0:0:2: Ending Domain Validation
Jul 18 16:29:39 localhost kernel:  target0:0:2: FAST-40 WIDE SCSI 80.0 MB/s ST (25 ns, offset 127)
Jul 18 16:29:39 localhost kernel: SCSI device sdc: 2097152 512-byte hdwr sectors (1074 MB)
Jul 18 16:29:39 localhost kernel: sdc: Write Protect is off
Jul 18 16:29:39 localhost kernel: sdc: cache data unavailable
Jul 18 16:29:39 localhost kernel: sdc: assuming drive cache: write through
Jul 18 16:29:39 localhost kernel: SCSI device sdc: 2097152 512-byte hdwr sectors (1074 MB)
Jul 18 16:29:39 localhost kernel: sdc: Write Protect is off
Jul 18 16:29:39 localhost kernel: sdc: cache data unavailable
Jul 18 16:29:39 localhost kernel: sdc: assuming drive cache: write through
Jul 18 16:29:39 localhost kernel:  sdc: unknown partition table
Jul 18 16:29:39 localhost kernel: sd 0:0:2:0: Attached scsi disk sdc
Jul 18 16:29:39 localhost kernel: sd 0:0:2:0: Attached scsi generic sg2 type 0

How Do I Delete a Single Device Called /dev/sdc?

In addition to re-scanning the entire bus, a specific device can be added or existing device deleted using the following command:
# echo 1 > /sys/block/devName/device/delete
# echo 1 > /sys/block/sdc/device/delete

How Do I Add a Single Device Called /dev/sdc?

To add a single device explicitly, use the following syntax:

# echo "scsi add-single-device <H> <B> <T> <L>" > /proc/scsi/scsi

Where,

  • <H> : Host
  • <B> : Bus (Channel)
  • <T> : Target (Id)
  • <L> : LUN numbers

For e.g. add /dev/sdc with host # 0, bus # 0, target # 2, and LUN # 0, enter:
# echo "scsi add-single-device 0 0 2 0">/proc/scsi/scsi
# fdisk -l
# cat /proc/scsi/scsi
Sample Outputs:

Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: VMware,  Model: VMware Virtual S Rev: 1.0
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
  Vendor: VMware,  Model: VMware Virtual S Rev: 1.0
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 02 Lun: 00
  Vendor: VMware,  Model: VMware Virtual S Rev: 1.0
  Type:   Direct-Access                    ANSI SCSI revision: 02

Step #3: Format a New Disk

Now, you can create partition using fdisk and format it using mkfs.ext3 command:
# fdisk /dev/sdc
### [if you want ext3 fs] ###
# mkfs.ext3 /dev/sdc3
### [if you want ext4 fs] ###
# mkfs.ext4 /dev/sdc3

Step #4: Create a Mount Point And Update /etc/fstab

# mkdir /disk3
Open /etc/fstab file, enter:
# vi /etc/fstab
Append as follows:

/dev/sdc3               /disk3           ext3    defaults        1 2

For ext4 fs:

/dev/sdc3               /disk3           ext4    defaults        1 2

Save and close the file.

Optional Task: Label the partition

You can label the partition using e2label command. For example, if you want to label the new partition /backupDisk, enter
# e2label /dev/sdc1 /backupDisk
See “The importance of Linux partitions

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51 comments… add one
  • Bram-NL Jul 18, 2009 @ 12:29

    To add a single device explicitly, use the following syntax:
    # echo "scsi add-single-device &lgt;H> " > /proc/scsi/scsi

    I guess “&lgt” should be “<" (<)

    Reply Link
  • 🐧 nixCraft Jul 18, 2009 @ 12:44

    @Bram-NL,

    Thanks for the heads-up!

    Reply Link
  • jok Jul 18, 2009 @ 20:30

    Very nice, thanks!

    Oh, and in Step #3, i guess, it should be:
    mkfs.ext3 /dev/sdc3
    (not mkfs.exr3).

    Reply Link
    • andre Sep 15, 2015 @ 12:48

      may be mkfs -t ext4 /dev/sdc3

      Reply Link
  • ashwani Jul 19, 2009 @ 15:44

    Thanks for very nice info
    can u please explain what it means “- – -” ??

    Reply Link
    • mh Feb 29, 2016 @ 9:09

      – – – = wild cards for Channel ID, SCI target ID and LUV

      Reply Link
  • 🐧 nixCraft Jul 19, 2009 @ 19:59

    @jok,

    Thanks for pointing out a typo.

    @ashwani,

    It is syntax for rescanning and nothing else.

    Reply Link
  • hillel Jul 20, 2009 @ 14:24

    With VMware and SAN storage devices it is possible to change the disk size. In windows rescan disks updates the new size. The only way I found to notify the OS (linux)that the disk geometry was changed is by rebooting. Is it possible to do this online?

    Reply Link
    • David van Laatum Dec 21, 2011 @ 3:23

      Exchange scan with rescan
      I usually use
      find /sys/ -name rescan -exec sh -c ‘echo 1 1 1 > {}’ ;

      Reply Link
  • michaelvino Jul 22, 2009 @ 10:31

    hi vivek
    Ur updates are really useful for me …I am Fresher now i m using rhel5.0 i forgot the steps to create the repositery can u help me…. In my home i didn’t have internet i used a system as a client i copied all the dvd contents into /var/ftp/pub/Server please help me …

    Reply Link
  • Andy Aug 11, 2009 @ 9:27

    Nice job! I’m sure this will save my bacon one day.

    Reply Link
  • trentlaceysunxxp Aug 20, 2009 @ 18:31

    I really liked it. But not bad, it would be to add a few important sections.

    Reply Link
  • antonio Aug 21, 2009 @ 22:26

    Very nice… saved my bacon! and my friday afternoon. Now I can go get some “real work” done… (ha!) and maybe even go home for dinner, instead of chasing IT people here.

    Reply Link
  • Erik Aug 31, 2009 @ 21:03

    Awesome, thanks.

    Reply Link
  • qubex Oct 24, 2009 @ 15:10

    Very nice article!
    I have a similar situation and this worked quite well.

    One question though.
    When you have a situation like described above, with /dev/sda1, /dev/sdb1 and /dev/sdc1; what happens when you detach /dev/sdb1, so only /dev/hda1 and /dev/hdc1 are left?
    I’ve experienced earlier that Linux has a way with reshuffeling its device-names after reboot. So I think you can expect /dev/sdc might change to /dev/sdb?

    Thanks, Q

    Reply Link
  • Low351 Oct 29, 2009 @ 14:04

    Thank you, this information helped me.

    Reply Link
  • radiodog Dec 4, 2009 @ 1:52

    Oh. Hi! 🙂 He stood there motionless and in wonder, dimly conscious that Brenson was speaking to him, but not catching the meaning of his words. Never mind that. Impossible!.
    Gonna be back soon 🙂

    Reply Link
  • Tiago Ferreira Dec 18, 2009 @ 15:11

    Very very useful.

    Nonetheless, /sbin/partprobe is not necessary/recommended?

    cheers

    TF

    Reply Link
  • brautkleiderIvy Jan 10, 2010 @ 3:05

    Hello from Zuerich,
    i just want to say that i like your website very much.
    I will come back soon.

    Yours Ivy

    Reply Link
  • arumon Feb 2, 2010 @ 12:05

    Really Good 🙂
    Thanks a lot !!!

    Rgds,
    Arumon

    Reply Link
  • Jimbo Mar 18, 2010 @ 11:39

    very cool to ‘hot-add’ virtual disks. Thanks for the info.

    Reply Link
  • Seb Mar 24, 2010 @ 16:07

    Thanks !

    Reply Link
  • Lakshmipathi Aug 4, 2010 @ 7:10

    Thanks,useful one.I like the rescan part!

    Reply Link
  • msawawa Sep 20, 2010 @ 9:16

    the rescan part doesnt seem to work on SuSE 10 Enterprise Linux SP3

    Reply Link
    • somnath Jan 25, 2011 @ 21:28

      The rescan does not work with RHEL 5 guest VMs when existing virtual disks are resized. It only recognizes the changed size after reboot. Is there any way this can be done online ?

      Reply Link
  • Shane Miller Feb 3, 2011 @ 17:26

    I am using cat /etc/*release
    SUSE Linux Enterprise Server 10 (x86_64)
    VERSION = 10
    PATCHLEVEL = 3
    LSB_VERSION=”core-2.0-noarch:core-3.0-noarch:core-2.0-x86_64:core-3.0-x86_64″

    This rescan works like a champ for me.

    Reply Link
  • Heherson Tan Mar 19, 2011 @ 12:15

    I’m using Centos 5.5. I can’t find it in /dev/

    ls /dev/sdd
    ls: /dev/sdd: No such file or directory

    but dmesg shows the new drive

    SCSI device sdd: 33554432 512-byte hdwr sectors (17180 MB)
    sdd: Write Protect is off
    sdd: Mode Sense: 5d 00 00 00
    sdd: cache data unavailable
    sdd: assuming drive cache: write through
    sdd: unknown partition table
    sd 0:0:3:0: Attached scsi disk sdd
    sd 0:0:3:0: Attached scsi generic sg3 type 0

    Reply Link
  • fsnikkijamesa2 Jun 16, 2011 @ 20:26

    Awesome web-site yours sincerely, Pauletta Mencia

    Reply Link
  • Suresh Sep 14, 2011 @ 16:32

    Excellent Work. Thanks a lot.

    Reply Link
  • Wallander Nov 22, 2011 @ 10:15

    Excellent post. Worked like a charm.

    Always Appreciated nixcraft blogs.

    Keep the great work going.

    Reply Link
  • Shaik Dec 10, 2011 @ 3:27

    Nice article. Thanks for the steps.

    Reply Link
  • Shery Jan 17, 2012 @ 7:16

    Great!.
    Like your articles..
    Always a direct hit!

    Reply Link
  • Bubba Apr 13, 2012 @ 16:55

    Thanks a million!! This was very helpful.

    Reply Link
  • Ashok Jun 7, 2012 @ 0:46

    thanks for your valuable stuff buddy

    Reply Link
  • james Sep 7, 2012 @ 10:42

    very useful and straight forward method for scaning new disks .

    Reply Link
  • RAMS Feb 7, 2013 @ 11:05

    Very useful stuff..

    Reply Link
  • Rajesh Jul 4, 2013 @ 9:30

    Great article, i was looking for this details. Well, explained.keep coming….

    Reply Link
  • okon Aug 28, 2013 @ 21:39

    thanks a lot.

    Reply Link
  • joe Dec 20, 2013 @ 11:47

    Pretty cool!

    Any directions for doing this on RHEL 6.5 on a VMWare(ext4)? Or would it be the same.

    Thanks

    Reply Link
  • Kuldeep Kulkarni Apr 20, 2014 @ 21:06

    Guyz,

    If you are facing problem in step number 2 then here is the solution :

    First find your host bus number

    grep mpt /sys/class/scsi_host/hostX/proc_name

    Which should return a line like

    /sys/class/scsi_host/hostX/proc_name:mptspi

    where hostX is the relevant field.

    use this to rescan the bus with the following command

    echo “- – -” > /sys/class/scsi_host/hostX/scan

    Reply Link
  • Alex May 29, 2014 @ 13:06

    You’re aways saving me!! Thanks a lot!!!

    Reply Link
  • ser tr Jun 20, 2014 @ 8:26

    great! thanks a lot 🙂

    Reply Link
  • Robert Sander Oct 14, 2014 @ 4:46

    rescan-scsi-bus.sh exists since 10 years for thus purpose.

    Reply Link
  • Jon Apr 13, 2015 @ 22:08

    It doesn’t hurt anything to rescan all the drives.

    echo “- – -” | tee /sys/class/scsi_host/*/scan

    All the rest of the information is good.

    Reply Link
  • Ivor Horton Apr 23, 2015 @ 14:01

    Could you explain the commands and not only type them?
    For example, for the following commands:
    echo “- – -” > /sys/class/scsi_host/host0/scan

    What does it really do? Can we change “- – -” to anything else like “test…” etc.? What if I have many “host#”? Which one should I use? In my system I have 34 this kind of things.

    Thanks.

    Reply Link
    • Karavis Sep 4, 2015 @ 15:33

      The three values stand for channel, SCSI target ID, and LUN. The dashes act as wildcards meaning “rescan everything”

      Reply Link
    • valery Feb 17, 2017 @ 10:18

      for i in $(echo `find /sys/class/scsi_host -name "host*"`); do echo "- - -" > ${i}/scan; done
      and for FC
      for i in $(echo `find /sys/class/fc_host -name "host*"`); do echo "1" > ${i}/issue_lip/; done

      Reply Link
  • RajBLR Aug 23, 2016 @ 15:40

    Thanks this soloved my problem.

    Reply Link
  • kiran Dec 17, 2016 @ 20:25

    # ls /sys/class/scsi_host
    output shows many hosts like
    host0 host1 host2 host3 host4 .. .. . .. . .. .. . . . ..host25

    So, we can’t scan each and every host. How to know exactly which host we need to scan????

    Reply Link
  • Modi P A Feb 21, 2017 @ 20:08

    Thanks sir, it solved my problem.

    Reply Link
  • Régis Jul 19, 2017 @ 5:43

    My Man, you’re the best!

    Reply Link

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