High Redundancy High redundancy provides three-way mirroring and requires at least three
failure groups within a disk group. The failure of disks in two out of the three failure groups is for
the most part transparent to the database users, as in normal redundancy mirroring.
Mirroring is managed at a very low level. Extents, not disks, are mirrored. In addition, each
disk will have a mixture of both primary and mirrored (secondary and tertiary) extents on each
disk. Although a slight amount of overhead is incurred for managing mirroring at the extent level,
it provides the advantage of spreading out the load from the failed disk to all other disks instead
of a single disk.
Disk Group Dynamic Rebalancing
Whenever you change the configuration of a disk group??”whether you are adding or removing
a failure group or a disk within a failure group??”dynamic rebalancing occurs automatically to
proportionally reallocate data from other members of the disk group to the new member of the
disk group. This rebalance occurs while the database is online and available to users; any impact
to ongoing database I/O can be controlled by adjusting the value of the initialization parameter
ASM_POWER_LIMIT to a lower value.
Not only does dynamic rebalancing free you from the tedious and often error-prone task
of identifying hot spots in a disk group, it also provides an automatic way to migrate an entire
database from a set of slower disks to a set of faster disks while the entire database remains
online.
Pages:
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212