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Home > Storage Technology Tips > Data storage management > Assessing the cost/benefit ratio for storage quotas |
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DATA STORAGE MANAGEMENT Assessing the cost/benefit ratio for storage quotasPaul Hilton 03.26.2002 Rating: -4.38- (out of 5)
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Considerations for implementing quotas
Every alternative provides solutions, but also has its own problems. Since the original article dealt with quotas, what are some of the considerations around quotas that storage administrators might want to think about before they commit to this alternative? (For more information on these types of quota considerations, see the sidebar to this story.) Another very important consideration involves calculating the potential costs or benefits to your organization for implementing quotas. This area is discussed in more detail below.
Identifying the costs and benefits involved in implementing quotas
There are costs involved with any storage management alternative, just as there are also costs involved with a status quo approach. Some of the costs involved with quotas include:
On the benefits side of the equation, quotas provide a mechanism to limit growth in portions of the storage subsystem. The savings accrue between the growth prior to quota implementation and the growth after quota implementation.
There may also be some administrative savings achieved through no longer having
How to calculate quota cost/benefit ratios
When trying to decide whether or not to implement a storage quota system, you might want to consider calculating the potential cost and benefits involved. The examples shown below are reasonably quick calculations to provide guidance. Every situation will be different.
Cost example
In reality, the costs don't scale directly with the storage added. Adding a tape drive or media to a tape library is less expensive than adding a new tape library. Utilizing part of another storage administrator is less expensive that adding a full storage administrator.
This example assumes a target environment of 200 users and 2T Bytes of disk storage. [TABLE]
In this example, the total yearly cost of adding quotas to this organization would be $151,000.
Benefit example:
The benefits example assumes the savings to the organization will come from the avoidance of purchasing additional disk and the management costs associated with managing the disk.
To calculate the benefit side, a burdened cost of storage could be calculated. This burdened cost of storage should include the yearly people cost to manage the target environment, plus the yearly capital cost of the storage devices (disk, tape, optical), plus the yearly cost of storage software, plus the yearly cost of floor space and power for the target environment.
The burdened-cost of storage would then be divided by the number of gigabytes in the target environment. This would result in a burdened cost per gigabyte per year. The projected savings, in gigabytes, from the quota system would be multiplied by the burdened cost per gigabyte per year to determine the benefits.
Extending the costs example, let's assume that a particular target system serves 200 users, with 2T Bytes of disk storage, an average of 10G Bytes per user. The system managers are considering implementing a quota system and hope to avoid an increase of 2G Bytes per user, or 400G Bytes of total upgrade. The inputs to the burdened storage cost are as follows: [TABLE]
The yearly total would be $263,000 per year. The burdened cost of storage per year is $263,000 divided by 2000G Bytes or about $132 per G Byte per year.
The yearly cost of adding 400G Bytes for the purposes of this example is 400G Bytes x $132 per G Byte per year (or $52,800).
Evaluating quota costs and benefits together to make a decision
In the above two examples, the benefit of not adding the 400G Bytes to the organization is $52,800. The cost of the quota system to the organization is $151,000. In this case, the costs of implementing a quota system exceed the benefits by almost $100,000.
If a decision was based on organization-wide cost/benefits, a quota system could not be justified.
About the author: Paul Hilton is an independent consultant who has worked with mainframe, UNIX and Windows-based storage systems for the past 25 years. During that time, he's worked for customers and service providers as a storage manager, capacity planner, architect and consultant and has both performed pre/post sales support and product management functions. In the early 90's, Hilton was also involved with GUIDE, an IBM users group, where he participated in a number of storage-related projects. He can be reached via e-mail.
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