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Root volume recommendations

The root volume can exist as either the traditional stand-alone two- or three-disk volume or as a FlexVol volume that is part of a larger hosting aggregate. There are considerations to keep in mind when choosing what kind of volume to use.

Smaller stand-alone root volumes offer fault isolation from general application storage, whereas flexible volumes have less impact on overall storage utilization, because they do not require two disks to be dedicated to the root volume and its small storage requirements.

If a FlexVol volume is used for the root volume, file system consistency checks and recovery operations could take longer to finish than with the two- or three-disk traditional root volume. FlexVol recovery commands work at the aggregate level, so all of the aggregate's disks are targeted by the operation. One way to mitigate this effect is to use a smaller aggregate with only a few disks to house the FlexVol volume containing the root volume.

In practice, having the root volume on a FlexVol volume makes a bigger difference with smaller capacity storage systems than with very large ones, in which dedicating two disks for the root volume has little impact.

The following list summarizes the facts and recommendations about root volumes:
  • Root volumes may use either flexible or traditional volumes.
  • For higher resiliency, use a separate two-disk root volume.
    Note: It is recommended that you convert a two-disk root volume to a RAID-DP volume when performing a disk firmware update, because RAID-DP is required for disk firmware updates to be non-disruptive. When all disk firmware and Data ONTAP updates have completed, the root volume can be converted back to RAID4.

    For Data ONTAP 7.3 and later, the default RAID type for traditional root volume is RAID-DP. If you want to use RAID4 as the raid type for your traditional root volume to minimize the number of disks required, you can change the RAID type from RAID-DP to RAID4 by using vol options vol0 raidtype raid4.

  • For small storage systems where cost concerns outweigh resiliency, a FlexVol based root volume on a regular aggregate may be more appropriate.
  • It is recommended that you avoid storing user data in the root volume, regardless of the type of volume used for the root volume.