Virtual diskstores

It is possible to start a system in which not all disk resources are available, for example when a disk has failed and cannot be recovered quickly. One way to do this is to have the system recreate data on demand from the parity information in the failed disks’s RAID cluster. These processes which recreate data on the fly are called virtual diskstores.

To activate virtual diskstores, first ensure that software RAID is being used. Then set the parameter virtual_diskstores=yes in the [boot options] section of the config file.

Now, if for each missing disk resource:

  • It is the only disk resource missing from its cluster

  • All other disk resources in that cluster are in either state 1 (good) or state 7 (recreating parity)

…then a “virtual” Disk-Store will be used for each missing disk resource, enabling the system to start up and run by making use of RAID parity information.

Note that the performance of the system will be impacted for disk-heavy queries whenever disk resources are missing and virtual diskstores are running.