Netapp Aggregate - Division of data between volumes

Brian B
Brian B used Ask the Experts™
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I have an aggregate with 8TB of total space that is used for a vFiler. I received some alerts that more than 90% of the aggregate is used. However, looking at the three volumes that make up this aggregate:

V1 - 1TB, 25% used
V2 - 1TB, 25% used
V3 - 8TB, 90% used

It appears that the data is not being spread across the available space and instead all the data is going on to V3.

I have inherited this Netapp like this, so I don't know if this is normal or not. I would assume that the Netapp OS would put more data on V1 and V2 before letting V3 fill up, but it doesn't seem to be this way so far? Is it bad or against best practice to let the aggregate volumes be different sizes like this?

Thanks!
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Paul SolovyovskySenior IT Advisor
Top Expert 2008

Commented:
The vfiler act as virtual Netapp controllers and do not distribute data.  The volumes that are attached to these vfilers sit on aggregates.  On which aggregate the corresponding volumes are being stored in?  The volumes may be in different aggregates which are independent of each other and do not share disks or a way to distribute data unless this is on the application level.
Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
It's one aggregate. If I look in the information about the aggregate, it shows me those volumes.

Although it might help, unfortunately I can't provide a screen shot for security reasons.
Paul SolovyovskySenior IT Advisor
Top Expert 2008

Commented:
It may be a single aggregate but you have multiple volumes in the aggregate.  These volumes may be using the capacity in the aggregate.  

1.  How large is your aggregate
2.  How much volume storage are you using?  Ensure that you have data+snapshots in the equation
3.  Ensure that the volumes are thin provisioned, otherwise the 1TB volume that is only 25% full will use the entire 1TB
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Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
1. Aggregate is 8TB
2. Volumes are being used as above. Volumes aren't used for anything else besides this aggregate.
3. Graph shows only 25% used on the volumes.
Paul SolovyovskySenior IT Advisor
Top Expert 2008

Commented:
So let's do the math:  The following volumes are on the aggregate and usage is as listed.

90% of 8TB =7.2TB
25% of 1TB = .25TB
25% of 1TB = .25TB
Total = 7.7TB which equal to 96.25% used on the aggregate which is what the Netapp is reporting.  You should not go over 90% as best practice.  If the aggregate is storing the volumes attached to the vfilers then you're running out of space.

What
Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
So I suspect that increasing B and C won't have any affect though. So it makes less sense to keep increasing A when B and C are not being fully utilized. IS there a way I can fix that?
Paul SolovyovskySenior IT Advisor
Top Expert 2008
Commented:
If the volumes are in the same aggregate it will not a difference.  The aggregate is your pool, the volumes that live in that pool are using all that's available, if you use the other volumes (and the're in the same aggregate) you will cause an outage when you run out of space on the aggregate.  The volumes are most likely thin provisioned and will allow you to oversubscribe.
Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
I didn't realize this question was still open, but I think I have found a better explanation as to why this is happening. Looking at the volumes in the aggregate it shows this:

Name, available space, total space
V1, 320GB, 1TB
V2, 320GB, 1TB
V3, 320GB, 8TB

In other words, the NETAPP controller is trying to balance the available space across the volumes, not the % used, despite the fact they are different sizes.

As I said, these are the only volumes in this aggregate.
Top Expert 2014

Commented:
Are you sure V1, V2 and V3 aren't disk groups?
The Netapp isn't trying to balance anything.

There's just one pool of free space that is being shared by all the volumes. This free space is handed out on a "First Come First Served" basis.

Let's say you have 700GB left. Any application/user that writes 700GB to either of the 3 volumes will cause the free space to be used up. And will cause all 3 volumes to be full at the same time, which will probably crash the applications that are using them and data to be lost.

The free space you see in each volume isn't guaranteed because it's the same shared free space you see in the other volumes. Don't try to add these numbers up, it will not make sense.

That being said, if your aggregate is really 90% full, you're in a dire situation. Because of the way Netapp works, you're likely to suffer performance loss with so little free space. Also, when space finally runs out, all volumes will be affected at the same time. Applications using the volumes will probably crash or stop working and data may be lost.

So I suggest you take action urgently.
Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
So what action to take? Will increasing the size of the smaller volumes actually change anything, since it's the larger of the three that is 90% full? What should be done to ensure the volumes are balanced optimally?
There is no "balancing" possible, full is full. The free space you see in the volumes is not there because the volumes are oversubscribed.

The volumes are using almost all of the physical storage space and changing sizes of any of the volumes or moving data between them does not change anything.

Several options:

- see if the largest volume contains any unnecessary data that can be deleted.
- especially have a look if there are any old snapshots on that volume that can be deleted. Old snapshots are often the reason why volumes fill up.
- get more physical storage space (disks) to extend the current aggregate
- move the largest volume to a larger aggregate, if available.
Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
"move the largest volume to a larger aggregate, if available"
There are unused disks available, but just to clarify... I thought that the aggregate was made up of volumes? So the size of the aggregate is already the size of the volumes? We then have a vfiler pointing to that aggregate to store data.
Top Expert 2014

Commented:
> I thought that the aggregate was made up of volumes?

I thought you were talking about RAID groups rather than volumes which is why I posted 41572694 previously.
Aggregates are made of groups of disks. Volumes are carved out of an aggregate.

Think of an aggregate as one big container that has several volumes inside.

Extending the aggregate will provide extra space that can be used by the volumes.
Brian BEE Topic Advisor, Independant Technology Professional

Author

Commented:
I was looking at the problem the wrong way around. I see now that volumes are not limited by the size of the aggregate in the way I thought. Adding disks solved the immediate problem by making the aggregate bigger, which gave more room for the volume to grow.

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