It must be understood that no system storage requirement estimation can be expected to maintain or have any kind of reliable accuracy. Future mail use, litigation requirements, and compliance standards all may change and are unpredictable at best. Micro Focus bears no responsibility to accurately define or recommend storage needs for various messaging systems. Different messaging systems have different storage characteristics, and individual implementation renders general calculations invalid.
Keep in mind, however, that storage-system performance dictates mail view, indexing, and data performance. If the storage system is housed on slow hardware employing a file system designed for any other consideration than speed, (e.g. compact data storage), performance may be impacted. Consider what types of files are to be archived and access frequency when choosing the file system. For example, a Retain system dealing with mainly or only archived mobile data (SMS, pin, MMS, &etc.) performs best with different file system settings than a Retain system archiving a message system with large attachments.
For best results; pair current mail storage needs against projected future needs with the ability to easily add extra storage to the Retain system as needed. The ability to freely add additional storage space grants control and freedom over the messaging system and should be of paramount consideration. This practice is the only course which can be relied on with any confidence. Due to the challenges and circumstances involved with each different system, (and even certain versions of different systems), only individual consideration provides a reliable baseline for storage needs.
The simplest way to check current disk usage and storage requirement size, is to monitor disk space usage on the mail servers and create a projection for the near future for needs. As a rule of thumb, we have noticed that message systems increase by about 11% per day.
However, the different options and variables between messaging systems make disk storage estimations so unpredictable that anything other than specific system monitoring cannot determine real disk usage. It is best to create a storage system where additional space may be added as required when existing space is consumed.
In addition, Exchange 2010 has abandoned single-instance storage in favor of highly available performance, possibly causing multiple Exchange servers in the system to all have copies of the same data. Retain utilizes single-instance storage and may vastly decrease the storage size of a system that heavily utilizes this feature. Due to the differences between the storage and main messaging system, it is nearly impossible to establish a baseline for Retain storage needs. Retain may tremendously decrease the needed size to archive an Exchange 2010 system, or, depending on system size and implementation, it may not significantly decrease the needs of the current system. Though Retain requires additional space to continue archiving mail, the initial archive job will not exceed the size of the current messaging system.
Consulting with the Retain Sales representative offers the best tailored information for each system and each implementation of the different platforms available.