A NetApp volume is composed of one or more NetApp RAID groups. From the perspective of gFilers, Data ONTAP uses RAID groups to determine where to allocate data to the LUNs. A gFiler RAID group is composed of one or more LUNs.
The default size of a RAID group is 8 LUNs. Typically, you would not change the default RAID group size. However, you need to change the default RAID group size if you want to add LUNs to the volume that are of a different size than the LUNs in the current RAID group; that is, the RAID group to which Data ONTAP is automatically adding LUNs to (see How Data ONTAP creates RAID groups automatically). This section provides details about RAID groups and provides information about how to change the RAID group size if you need to.
Note
Current in this context means the RAID group to which LUNs are being added.
The following table shows metrics for RAID groups.
|
400 RAID groups (applies to both clustered gFilers and a single gFiler) |
Caution
Exceeding the maximum volume size or maximum capacity for a gFiler model limits the maximum RAID groups in a volume.
When you create a volume or add LUNs to a volume, Data ONTAP creates new RAID groups as each RAID group is filled with its maximum number of LUNs, according to the raid-group-size parameter in the vol command. Within each volume, RAID groups are named rg0, rg1, rg2, and so on, in order of their creation. The last RAID group formed might contain fewer LUNs than are specified for the volume's RAID group size. In that case, any LUNs added to the volume are also added to the last RAID group until the specified RAID group size is reached.
Note
When creating a volume, you can use the -r raid-group-size command to specify the number of LUNs per RAID group. If no RAID group size is specified, the default value for your gFiler model is applied.
To avoid a performance penalty, you want all LUNs in a particular RAID group to be the same size. Therefore, when you want to add a LUN of a different size to a volume, you need to stop the current RAID group from growing beyond its current size (as would automatically occur if there is still room) and force a new RAID group to be created that would contain the LUNs of the different size. You can use the volume option named raidsize to limit the size the current RAID group to the number of LUNs already in it and to force a new RAID group to be created for newly-added LUNs. See Changing the size of the current RAID group.
Your goal should be to keep the default RAID group size of 8. After forcing a new RAID group to be created for the LUNs of the different size, stop the new RAID group from expanding beyond the LUNs of the different size, then set the RAID group size back to 8. Future RAID groups then contain 8 LUNs. Follow the procedure in Changing the size of the current RAID group for both stopping the RAID group size for the new, different-sized LUNs and returning to the default size of 8.
You can use the raidsize volume option to set the maximum RAID group size that can be reached when LUNs are added to a volume.
RAID groups that became full at a specific RAID group setting remain whatever size they were before the raidsize setting was changed.
To change the raidsize setting for a RAID group in an existing volume, complete the following step.
To verify the size of raidsize setting in a volume, enter the vol options vol_name command.
Another way to increase the size of an existing RAID group is to use the -g raidgroup option in the vol add command
If a volume has more than one RAID group, you can specify the RAID group to which you are adding LUNs. Typically you don't need to use this procedure, except if your RAID groups contain different size LUNs and the RAID groups are not yet full.
To add new LUNs to a specific RAID group of a volume, complete the following step.
Note
The number of LUNs you can add to a specific RAID group is limited by the raidsize setting of the volume to which that group belongs.
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Part No. 210-00661
File: manage3.htm
Last updated: 04/13/04 09:26:46