Unitek NetApp Training Blog

Traditional volumes in Data ONTAP 7.0

In my previous entry I discussed RAID groups and aggregates in the context of flexible volumes.  For the sake of completeness, I am now going to discuss traditional volumes.  This should not be taken as an endorsement.  You should be using flexible volumes.  They have many significant advantages over traditional volumes.  Flexible volumes were introduced in Data ONTAP 7.0 and hopefully by now everyone has converted over to them.

In Data ONTAP 7.0, the concept of aggregates and flexible volumes were introduced. The older traditional volumes had dedicated RAID groups that belonged to the volume.  In effect, the aggregate was implied.  In Data ONTAP 7.0 and later we see this implemented.

I have created a traditional volume on my simulated filer.  I used the following command to create this volume:

vol create 3

Notice what happens if I do an aggr status:

The traditional volume is listed as an aggregate.  Notice what happens after a vol status command:

Vol 3 is also listed as a volume.  So a traditional volume has the qualities of an aggregate and the qualities of a volume.

Let’s take a look at the output of sysconfig –r:

Look at /vol3/plex0/rg0.  You can see that vol3 has its own dedicated RAID group.

This is what defines a traditional volume.  It is both an aggregate with associated disks that are assigned to RAID groups and a volume that presents logical storage for applications to access through a protocol stack.

Notice also that it has a single parity disk.  By default, traditional volumes use RAID-4 rather than RAID-dp.  This makes sense when you consider that by dedicating RAID groups to each volume you are more likely to have smaller RAID groups and more numerous RAID groups.

You can see from this the great advantage of aggregates and flexible volumes.

Instead of dedicating disk spindles to a volume I can group a large number of disks to an aggregate.  Then I can assign a volume to that aggregate, reserving exactly the amount of space that it needs, rather than a multiple of the drive size.  My volume will have better performance, because its I/O demands are spread over a large number of disks.  Many volumes can share the space available in the aggregate which provides a large pool of iops that all the volumes draw from.

Also, by building larger RAID groups and then protecting those RAID groups with two parity drives, the aggregate potentially improves efficiency (possibly fewer parity drives needed in total) and provides greater protection when a drive fails.