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Zero downtime storage migration operations

January 27th, 2011 by TheBonsai

For some systems a downtime is complicated to organize, or bad at all. We have such a system, a RAC database.

In the past, all storage migration operations there had two problems that lead to downtime:

  • CRS votedisk migration at best only with offline CRS
  • kick old devices from the device management in the operating system

In December I migrated the system to something more modern

  • SLES11
  • Oracle Grid Infrastructure (CRS/ASM) 11.2
  • Oracle Database 10.2.0.5 (yes, still quite old, but it has to be a 10.2 for now)

The use of a modern Linux kernel (especially a modern SCSI stack) and 11gR2 infrastructure fixed all my trouble from the past.

Votedisk

With 11gR2 Grid Infrastructure, the clusterware manages its vital files (VD, OCR) using an ASM instance. A migration of the ASM diskgroups holding these files is now as easy as a migration of a normal diskgroup. ASM takes care of moving the votedisks and the OCR and collaborates with CRS here.

Linux devices

The new Linux kernels with a finally sane SCSI stack and native multipathing helps with the second problem. It’s not a problem anymore to remove old device references from the stack:

  • deconfigure the devices from multipathd (not needed technically, since multipathd itself holds no device references)
  • remove the device references from the Linux device mapper
    # see /dev/mapper/* for the name
    # an alternative and probably more safe is: multipath -F (flush all unused maps)
    dmsetup remove mpathX
  • remove the LUNs from the SCSI stack
    # X:X:X:X LUN number
    echo 1 > /sys/bus/scsi/X:X:X:X/delete

After that, you can safely edit the FC zone – no errors should occur in any logs.

This entry was posted on Thursday, January 27th, 2011 at 07:18 and is filed under english, Oracle, Work. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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