IBM N Series, Hardware Manual

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IBM System Storage N series Hardware Guide
򐂰 Mailbox limit
The mailbox limit usually represents the quota that is assigned to users for their mailboxes.
If you have multiple quotas for separate user groups, this limit represents the average.
This average, which is multiplied by the number of users, determines the initial storage
space that is required for the mailboxes.
򐂰
I/O load per user
For a new installation, it is difficult to determine the I/O load per user, but you can estimate
the load by grouping the users. Engineering and development tend to have a high
workload because of drawings and technical documents. Legal might also have a high
workload because of the size of legal documents. However, normal staff usage consists of
smaller sized I/O, more frequent transaction workloads. Use the following formula to
calculate the usage:
IOPS/Mailbox = (average disk transfers/sec) / (number of mailboxes)
򐂰 Concurrent users
Typically, an enterprise’s employees do not all work in the same time zone or location.
Estimate the number of concurrent users for the peak period, which is usually the time
when the most employees have daytime operations.
򐂰 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 that is used affects
performance and capacity.
򐂰 Drive type
Earlier, this chapter described 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.