What Does /MissingDisk Entry In 'disktab' File Signify?

Document created by mufeed on Feb 7, 2016
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Author: Mufeed Usman

 

Original Publication Date: July 16, 2015

Symptom:

/opt/mapr/conf/disktab file shows "/_MissingDisk" entry, for example:

/dev/sdf D327FEA2-7AA8-EBAC-6427-0F864EE05400 
/dev/sdg FE43D6EC-CAB9-3417-728C-00874EE05400
/_MissingDisk6 C4A81253-7B7E-57FB-A037-01874EE05400
#/dev/sdi 16306743-F9EB-CE71-A5E4-01874EE05400

Root Cause:

This happens when disk names (paths) change.

MFS process tries to fix disktab file by looking for disks in /proc/partitions. If a particular disk corresponding to a GUID is missing and the old disk path now corresponds to a different disk GUID, MFS process fixes disktab by replacing the disk path of missing disk with "_MissingDiskX" entry.

Solution:

If the disk corresponding to this GUID is permanently lost, just delete/comment the line corresponding to it in disktab and restart MFS.

"maprcli disk remove _MissingDisk6" should also work for the above scenario. Check the exact path in disktab file.

MFS process is responsible for checking the disk GUID and updating the disktab file. This happens with every restart of the MFS service and is not continuously monitored.

 

To manually verify the disk GUID and compare it with disktab one can do the following steps.

  • Add the list of all disks that you'd like GUID generated for in a file, say, "list"; one disk per line
  • Then run,
[root@n73 server]# /opt/mapr/server/disksetup -G list # MapR Disks Fri Mar 27 17:42:15 2015  

/dev/sdb 0DFA170C-0119-29BD-9106-0CB781B85400
/dev/sdc 0ECFAA24-7ECB-6E92-E455-0EB781B85400
/dev/sdd C07794F1-03F2-1C19-C1FA-00B881B85400

 

And you can verify/cross-check the same with the values in /opt/mapr/conf/disktab as,

[root@n73 server]# cat /opt/mapr/conf/disktab

# MapR Disks Fri Jan 16 08:43:05 2015 /dev/sdb 0DFA170C-0119-29BD-9106-0CB781B85400

 

/dev/sdc 0ECFAA24-7ECB-6E92-E455-0EB781B85400 /dev/sdd C07794F1-03F2-1C19-C1FA-00B881B85400

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