Backup Servers; Backup And Recovery - IBM N Series Hardware Manual

Number of storage groups
Because a storage group cannot span N series storage systems, the number of storage
groups affects sizing. There is no recommendation on number of storage groups per IBM
System Storage N series storage system. However, the number and type of users per
storage group helps determine the number of storage groups per storage system.
Volume type
Are FlexVols or traditional volumes used? The type of volume used affects both
performance and capacity.
Drive type
Earlier, this chapter addressed the storage capacity effect of drive type. For Microsoft
Exchange, the drive type and performance characteristics are also significant, especially
with a highly used Exchange server. In an active environment, use smaller drives and
higher performance characteristics such as RPM and Fibre Channel versus SATA.
Read-to-write ratio
The typical read-to-write ratio is 70% to 30%.
Growth rate
Industry estimates place data storage growth rates at 50% or higher. Size for at least two
years into the future.
Deleted mailbox cache space
This is a feature of Microsoft Exchange that must also be sized for storage usage on the
N series. Microsoft allows for a time-specified retention of documents even after deletion
of a mailbox. You also must size the storage effect of this feature.

14.2.8 Backup servers

Protecting and archiving critical corporate data is increasingly important. Deploying servers
for this purpose is becoming more common, and these configurations call for their own
planning guidelines.
A backup server generally is not designed to deliver high transactional performance. Data
center managers rely on the backup server being available to receive the backup streams
when they are sent. Often the backup server is an intermediate repository for data before it
goes to backup tape and ultimately offsite. But frequently the backup server takes the place of
backup tapes.
The write throughput of a backup server is frequently the most important factor to consider in
planning. Another important factor is the number of simultaneous backup streams that a
single server can handle. The more effective the write throughput and the greater the number
of simultaneous threads, the more rapidly backup processes complete. The faster the
processes complete, the sooner that production servers are taken out of backup mode and
returned to full performance.
Each IBM System Storage N series platform has different capabilities in each of these areas.
The planning process must take these characteristics into account to ensure that the backup
server is capable of the workload expected.

14.2.9 Backup and recovery

In addition to backup servers, all storage systems must be backed up. Generally, the goal is to
have the backup process occur at a time and in a way that minimizes the effect on overall
production. Therefore, many backup processes are scheduled to run during off-hours.
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IBM System Storage N series Hardware Guide