Tag: rhel

Can I safely ignore I/O errors on dm devices?

The root user of a system using may occasionally receive a message similar to the following in the daily logwatch email:

--------------------- Kernel Begin ------------------------

WARNING:  Kernel Errors Present
    Buffer I/O error on device dm-7,  ...:  11 Time(s)
    EXT3-fs error (device dm-7): e ...:  90 Time(s)
    lost page write due to I/O error on dm-7 ...:  11 Time(s)

Likewise, you may notice similar error messages in the /var/log/messages file:

May 16 04:04:52 eclipse kernel: lost page write due to I/O error on dm-20       
May 16 04:04:52 eclipse kernel: Buffer I/O error on device dm-20, logical block 0
May 16 04:04:52 eclipse kernel: lost page write due to I/O error on dm-20       
May 16 04:04:52 eclipse kernel: Buffer I/O error on device dm-20, logical block 0
May 16 04:04:52 eclipse kernel: lost page write due to I/O error on dm-20       
May 16 04:04:52 eclipse kernel: Buffer I/O error on device dm-20, logical block 0
May 16 04:04:52 eclipse kernel: lost page write due to I/O error on dm-20

If the device mapper (dm-n) device(s) mentioned in the messages refer to a snapshot logical volume (LV), these messages can be ignored. By their definition, snapshot LVs are temporal in nature; they are created, destroyed and expire when changes written to them exceed their predefined capacity.

To determine if the dm device points to a snapshot LV:

First, locate the “dm” device number in the logs (in our example, 20):

[root@eclipse ~]# grep "I/O error" /var/log/messages
May 16 04:04:52 eclipse kernel: Buffer I/O error on device dm-20, logical block 1545
May 16 04:04:52 eclipse kernel: lost page write due to I/O error on dm-20

Next, list the /dev/mapper/* devices, noting the minor device numbers of each, which correspond with the “dm” device number (in our example, 20):

[root@eclipse ~]# ls -l /dev/mapper/ | grep 20
brw-rw---- 1 root disk 253, 20 May 16 14:00 datavg-lvol1

Finally, list the LVs in the noted volume group to determine whether or not it’s a snapshot, signified by the “s” in Attr column and presence of Origin and Snap% values:

[root@eclipse ~]# lvs datavg
  LV       VG     Attr   LSize   Origin   Snap%  Move Log Copy%  Convert
  eclipse  datavg owi-ao 395.00G                                        
  ereports datavg owi-ao   1.00G                                        
  lvol0    datavg swi-ao   1.00G u2         0.41                        
  lvol1    datavg swi-ao  34.82G eclipse    0.74                        
  lvol2    datavg swi-ao   1.00G ereports   0.00                        
  lvol3    datavg swi-ao   3.61G pdw        0.01                        
  pdw      datavg owi-ao  45.00G                                        
  u2       datavg owi-ao   4.00G                                        
  uvtmp    datavg -wi-ao   4.00G

In our example, the Origin LV is /dev/datavg/eclipse, and the dm-20 device referenced in the error messages is indeed a snapshot LV.

If the dm-n device(s) mentioned in the messages do not refer to a snapshot logical volume (LV), you may have a filesystem, software or hardware issue, and you should contact your Red Hat support provider.

How do I verify my RHEL subscription details?

To verify the status of your Red Hat Enterprise Linux subscription and any technical support that you’re entitled to:

Log into the Red Hat website to access the subscriptions page: https://access.redhat.com/wapps/support/protected/subscriptions.html

If you have lost your Red Hat login credentials, please refer to this page.

Select the appropriate subscription from the table:

The details page will show the contract number, start and end dates, and which level of support is included:

If you have any further questions, please refer to How do I contact Red Hat for support? or email customerservice@redhat.com.

How do I install Red Hat Enterprise Linux updates?

Any time the kernel is upgraded, you’ll need to recompile and reinstall the drivers. As such, it is important to plan your kernel upgrades in advance and perform testing after the first boot using a new kernel.

To download and install all updates:

  • Log into your server as root
  • Run the following command:
yum -y update

References:

How do I contact Red Hat for support?

There are a couple different methods for contacting Red Hat:

Please provide the following to speed up your support request:
  • Your Red Hat Network username, customer number or contract number
  • A detailed description of your support request
  • Your complete contact information
  • The file generated by the “sosreport” command