||Oracle Tips by Burleson
Oracle10g Grid Computing
Chapter 12 - RAC Design Considerations
Failure of the Fabric Switch
fabric switch allows multiple hosts to access the SAN array. Failure
of the fabric switch (or other interconnect equipment) can result in
loss of performance or total loss of the application. If the SAN
cannot be accessed then the database will crash and no one will be
able to access it, even if all other equipment is functional.
can come in many forms. Catastrophic failure will, of course, result
in total loss of the database. Failure of a single drive, if there is
no hot spare or if the
hot spare has been utilized, will result in severe performance
degradation (by as much as 400-1000 percent) in a RAID5 situation
where the data on the failed drive has to be rebuilt on the fly from
parity information stored on the other drives in the RAID5 set. Even
if there is an available "hot" spare, it still takes time to rebuild
this hot spare from the parity data on the other drives. During this
rebuild performance will suffer.
SANs are configured with disk trays or "bricks" of a specific number
of drives (usually 8 active and a single spare in each tray or brick).
A single tray becomes an array, in the case of a RAID0+1 setup, the
array will be striped across the 8 drives and would be mirrored to
another tray in the array. Failure of a RAID0+1 drive has little
effect on performance, as its mirror drive takes over while the hot
spare is rebuilt on an "on available" basis. In a RAID5 array, the 8
drives are usually set up in a 7+1 configuration (7 drives in a stripe
set and one parity drive).
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