2 Iron

Problems to undertand Quota on Data Domain

Hi everyone

I've got some issues to understand the quota approach on Data Domain systems. I would like to create differente Mtrees for different departmens and each department is backing up different VMs and data to the data domain for example finance server, database server, file server etc.

They ask me know, tell me what is the maximum amount of data I am allowed to backup to your data domain. I check my Data Domain which is a small 2200 with 6.7 TB of netto capacity.

I don't know yet what is the compression (local or global) of their data on my data domain, I can just assume it. Let's say conservative 1:5 which means if they have 1TB of data I guess it consumes 250 Gbyte initially and based on their change rate it is going to incrase over time.

Well I check my data domain now and check my mtree "Finance" I can create a Quota on "Finance" but it is asking me for "Pre-Comp Soft Limit" and "Pre-Comp Hard Limit". AND this is what I don't get, I am interested in to know when is my Data Domain physically full and not logically.

Lets say I have 6.7 TB of physically capacity and i have 3 departments so I would like to give equally to them 2 TB of physical capacity resp. Quote. Based on my assumption of 1:5 I know this has to be 10 TB of logical data which my department can save.

But why is Data Domain asking me for a logical value??? Do I have to calculate down and say ok 10 TB devided by expected 5 it's 2 TB physical usage? Well I don't like that approach because for ME it is not logical, well maybe because I am too stupid.

Can we set physical capacity quota per mtree? I am happy for any input and explanation.


Tags (1)
2 Replies
2 Iron

Re: Problems to undertand Quota on Data Domain

Hi Duker,

          Below is the excerpt from the Administration guide.

MTree quotas apply only to the logical data written to the MTree. An administrator can set

the storage space restriction for an MTree, Storage Unit, or VTL pool to prevent it from

consuming excess space. There are two kinds of quota limits: hard limits and soft limits.

You can set either a soft or hard limit or both a soft and hard limit. Both values must be

integers, and the soft value must be less than the hard value.

When a soft limit is set, an alert is sent when the MTree size exceeds the limit, but data

can still be written to it. When a hard limit is set, data cannot be written to the MTree

when the hard limit is reached. Therefore, all write operations fail until data is deleted

from the MTree.

So, you can take an conservative Approach of 1:5 and assign the quotas or divide the actual capacity based on your needs.

2 Iron

Re: Problems to undertand Quota on Data Domain

I understand your situation #duker but this is how the DDOS is designed. you cannot define a Soft / hard quota limit on the post compressed data. As per my understanding the reason is it does not perform the deduplication on the MTree level, it performs it on the entire file system level, so calculating post comp on a particular MTree does sounds so great.

In your example if you think in your environment you may get 1:5 dedup rate then for a expected 2 TB of post compression capacity you can set a soft quota @ 8 TB and hard quota @ 10TB easily which helps you to achieve your goal. but there is no way you can set a soft / hard quota on post comp capacity of each MTree.

Hope this helps


please like / resolve on my post if you find it worth of doing.