How to add/update partition table without reboot

Jephe Wu -

Objective:  update partition table without Linux OS reboot
Environment:  RHEL 6.X
Tools: partprobe, partx -a , kpartx -a, blockdev --rereadpt /dev/sdX, sfdisk -R /dev/sdX, hdparm -z /dev/sdX

Concepts: create/update partition for a block device while Linux is running



In RHEL 6, it will only trigger the OS to update the partitions on a disk that none of its partitions are in use (e.g. mounted). If any partition on a disk is in use, partprobe will not trigger the OS to update partitions in the system because it is considered unsafe in some situations.

# partx -v -a /dev/sdb
# partx -l /dev/sdb


kpartx -a /file/path/system.img

mount /dev/loop0p1 /mnt/somewhere
Some raw images contains multiple partitions (e.g. full HD image). In this case, it's necessary to specify a starting offset for each partition

Some raw images contains multiple partitions (e.g. full HD image). In this case, it's necessary to specify a starting offset for each partition. offset is the bytes which is the starting sectors*512.

[root@ovm01 xen]# file system.img 
system.img: x86 boot sector, GRand Unified Bootloader (0.94); partition 1: ID=0x83, active, starthead 0, startsector 2048, 208896 sectors; partition 2: ID=0x83, starthead 0, startsector 210944, 20760576 sectors; partition 3: ID=0x82, starthead 63, startsector 20971520, 4194304 sectors, code offset 0x48

# mount -t vfat -o loop,offset=$((2048*512)),ro,noexec img.dd /mnt/tmp_1
# mount -t vfat -o loop,offset=$((210944*512),ro,noexec img.dd /mnt/tmp_2

# kpartx -v -a rawimage.dd
creates these mappings


The partitions can be mounted with these commands:
# mount /dev/mapper/loop0p1 /media/suspectHD_01/ -o ro
# mount /dev/mapper/loop0p5 /media/suspectHD_02/ -o ro

References commands

  • partx -va /dev/sdX
  • kpartx -va /dev/sdX
  • hdparm -z /dev/sdX
  • sfdisk -R /dev/sdX

How to increase Oracle ASM disk group size

Jephe Wu -

Objective:  increase existing ASM disk group size
Environment: RHEL 6.4 64bit, Oracle, iscsi, multipath, udev and ASM, EMC storage
Concept:  increase disk group size by increasing ASM disk size itself or adding some more ASM disk

Part I: Add additional Lun as ASM disk

1. create a new Lun in EMC storage
2. use the following methods to find out the newly created disk name ,e.g. /dev/sdae etc

more /proc/partitions  (the new lines at the bottom)
ls -l /sys/block
ls -l /dev/disk/by-uuid/

3. find out the WWID
scsi_id --whitelisted --replace-whitespace –-device=/dev/sdae
multipath -ll 

4. vi /etc/multipath.conf to use alias for newly added ASM lun, e.g. db1
then run multipathd reload to reload the configuration

4. find out the lunid and wwid for each Lun so we know which volume is which

It's best to get lunid from storage administrator so that we can confirm which volume is which, otherwise, try to run the following command to find out. If sg_inq command is not available, yum install sg3_utils first

for x in /dev/dm-* ; do export lunid=$( /usr/bin/sg_inq --page=0x83 ${x} | grep "^ 00" | cut -d" " -f17 | awk '{ print strtonum( "0x" $1 ) };' ) ; export wwid=$( /sbin/scsi_id --whitelisted --replace-whitespace --device=${x} ) ; echo ${lunid} == ${x} == ${wwid}; done

5. As the root user, identify the Device Mapper Universally Unique IDentifier (DM_UUID)
for each device mapper volume. The example below shows the DM_UID for the
partitions of the volumes labeled db1,db2,fra, and redo. 

# for i in db1p1 ; do printf "%s %s\n" "$i" "$(udevadm
info --query=all --name=/dev/mapper/$i | grep -i dm_uuid)"; done

db1p1 E: DM_UUID=part1-mpath-3600c0ff000d7e7a899d8515101000000
6. Create a file labeled 99-oracle-asmdevices.rules within /etc/udev/rules.d/

7. Within 99-oracle-asmdevices.rules file, create rules for each device similar to the
example below:

  • If one has made a change and don't want to reboot the system then can utilize udevadm trigger instead. Specify --type and--action or it will effectively work like start_udev.
 # /sbin/udevadm trigger --type=subsystems --action=add
 # /sbin/udevadm trigger --type=devices --action=add
 # /sbin/udevadm trigger --type=subsystems --action=change
 # /sbin/udevadm trigger --type=devices --action=change
  • One can even trigger only specific devices like below;
 # echo change > /sys/block/sda/sda1/uevent

8. make partition for new Lun, only run on one of RAC node if any
# parted /dev/mapper/db1 mklabel gpt mkpart primary "1 -1"
Information: You may need to update /etc/fstab.

Once the partition is created, a newly created device mapper device is created as db1p1.
# ls -l /dev/mapper/db1p1 
lrwxrwxrwx. 1 root root 8 Apr 16 15:15 /dev/mapper/db1p1 -> ../dm-11

NOTE: A newly created partition requires the alias name followed by p1 such as db1p1 seen
above. If p1 is missing, please run the following command to add the partition mappings to
the device mapper disks.
# kpartx -a /dev/mapper/db1

9.  if there's multiple paths on one system, you might need to run partprobe to update all available path for created partitions, and also run kpartx -a /dev/mapper/db1 on another RAC node
10. add partitioned new disk into disk group by CLI or asmca through vnc/xterm or ssh -X

Part II:  increase existing Lun size

1. increase size of one of LUNs on storage 
2. make OS recognize the new size 
To re-scan logical units on a system that uses multipathing, execute the aforementioned command for each sd device (i.e. sda, sdb, and so on) that represents a path for the multipathed logical unit. To determine which devices are paths for a multipath logical unit, use multipath -ll; then, find the entry that matches the logical unit being changed. It is advisable that you refer to the WWID of each entry to make it easier to find which one matches the logical unit being changed.
echo 1 > /sys/block/sdax/device/rescan
echo 1 > /sys/block/sday/device/rescan
echo 1 > /sys/block/sdaz/device/rescan
echo 1 > /sys/block/sdba/device/rescan

Instead you can use /usr/bin/ script for rescanning all SAN LUNs. The sg3_utils package provides the script, which can automatically update the logical unit configuration of the host as needed (after a device has been added to the system). The script can also perform an issue_lip on supported devices. For more information about how to use this script, refer to --help.

Now, run multipath -F followed by multipath -v2 mpathX to reload the mutipath configuration.

If the LUNs are configured over iSCSI protocol, the following command can be used to get the new LUN size:
# iscsiadm -m session -R

3. If it's multipath device, run kpartx -a /dev/mapper/mpathX if necessary
4. multipathd -k"resize map <multipath_device>"
5. reload multipath configuration : multipathd reload or multipathd restart, then run miltipath -ll to see new size.
Note: if you enabled 'queue if no path' option, then do not use multipathd -k'resize map mpatha'
6. resize /dev/mapper/mpathX by running resize2fs if necessary
7. check and resize ASM disk group
select name, total_mb, usable_file_mb from v$asm_diskgroup;
alter diskgroup DATADG resize all;