User`s guide

72 Chapter 5 Configuring the XStack Storage
5. Use the slider bars to select the access bandwidth and storage efficiency (if displayed)
desired for this volume. The values allowed for each ranges from 0-10. Their meaning, and
usage is as follows:
– Access Bandwidth Weight: This setting is a measure of how much bandwidth the volume
will use (i.e., how much initiator I/O activity can be expected for the volume). A large
number indicates more I/O. It also means the Administrator wants the initiators to
achieve fast access to the volume, compared to the other volumes stored on the XStack
Storage unit. A large value causes the XStack Storage unit to choose a larger number of
stripe members. The method used by the XStack Storage unit to select the organization
and number of members is described in
Table 5-1.
Table 5-1. Volume Organization and Members Based on Redundancy and Access Bandwidth Weight
Redundancy Access Bandwidth Weight Value
0 1 Large Values
None JBOD organization (1 member) Stripe organization with 2
members
Stripe organization with more members
Mirror Mirror organization (2 members) Stripe Mirror organization with 2
stripe members
Stripe Mirror organization with more
stripe members
Parity Parity organization with at least 3
members
In combination with the Storage Efficiency Hint, this selects Parity
organization with more members
In the Stripe Mirror organization, there are always two members for each
stripe member to allow for the duplicate copy of the data.
– Storage Efficiency Hint: When Parity is selected for Data Redundancy, this additional
setting allows the Administrator to further tailor the XStack Storage’s selection of the
member count. A large value tells the XStack Storage unit that the Administrator wants
to use disk space more efficiently (i.e., use less space for redundancy data). As a result,
a large value for this hint requests a larger number of members (which costs less space
for parity overhead).
Both Access Bandwidth Weight and Storage Efficiency Hint can be left at their default
settings of 5. These settings produce good volume organizations for each redundancy
setting that use some, but not for all XStack Storage’s drive resources.
If you change the default value for either setting, the number of members chosen for the
volume depends on the number of drives available at the time the volume is created.
Small settings tend to use a small number of members. As the setting values increase, the
number of members will increase slowly. When the values reach their maximum, the
XStack Storage unit will use all possible drives in the volume’s pool and the Available
Pool for a volume. (The spare count is the only limit to the number of drives that can be
obtained from the available pool.)