System information
1. Dump the device mapper table for the multipathed device using:
d msetup tabl e multipath_device
2. Save the dumped device mapper table as table_name. This table will be re-loaded and
edited later.
3. Examine the device mapper table. Note that the first two numbers in each line correspond to
the start and end sectors of the disk, respectively.
4. Suspend the device mapper target:
d msetup suspend multipath_device
5. Open the device mapper table you saved earlier (i.e. table_name). Change the second
number (i.e. the disk end sector) to reflect the new number of 512 byte sectors in the disk. For
example, if the new disk size is 2GB, change the second number to 4194304.
6. Reload the modified device mapper table:
d msetup rel o ad multipath_device table_name
7. Resume the device mapper target:
d msetup resume multipath_device
For more information about multipathing, refer to the Red Hat Enterprise Linux 6 DM Multipath guide.
25.14 .4 . Changing t he Read/Writ e St at e of an Online Logical Unit
Certain storage devices provide the user with the ability to change the state of the device from
Read/Write (R/W) to Read-Only (RO), and from RO to R/W. This is typically done through a
management interface on the storage device. The operating system will not automatically update its
view of the state of the device when a change is made. Follow the procedures described in this
chapter to make the operating system aware of the change.
Run the following command, replacing XYZ with the desired device designator, to determine the
operating system's current view of the R/W state of a device:
# bl o ckd ev --g etro /d ev/sd XYZ
The following command is also available for Red Hat Enterprise Linux 6:
# cat /sys/bl o ck/sd XYZ/ro 1 = read -o nl y 0 = read -wri te
When using multipath, refer to the ro or rw field in the second line of output from the mul ti path -l l
command. For example:
36001438005deb4710000500000640000 dm-8 GZ,GZ500
[size=20G][features=0][hwhandler=0][ro]
\_ round-robin 0 [prio=200][active]
\_ 6:0:4:1 sdax 67:16 [active][ready]
\_ 6:0:5:1 sday 67:32 [active][ready]
\_ round-robin 0 [prio=40][enabled]
\_ 6:0:6:1 sdaz 67:48 [active][ready]
\_ 6:0:7:1 sdba 67:64 [active][ready]
Red Hat Ent erprise Lin ux 6 St orage Admin ist rat io n G uide
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