I see the ASM "allocation_unit_size" columns in the
v$asm_diskgroup table, but I don't understand the
relationship between the allocation unit (AU) size and the
stripe size. Is the stripe size the same as the AU
size. If so, what is the difference between the
find-grained stripe size and the coarse-grained stripe size?
"stripe size" is the number of "contiguous data blocks" on
each physical disk and from this quote, they appear to be
the same thing. Note that stripe size = stripe depth.
Oracle notes that it is the ASM
allocation Unit determines the unit of ASM storage (i.e.
size of file extent , also called as stripe depth) and the
stripe depth defaults to 1M.
When Oracle ASM stripes
data, Oracle separates the data file into stripes and deals
then evenly, out across each physical disk spindle.
"The stripes are equal in size to the
effective AU. The coarse-grained stripe size is always equal
to the AU size.
The fine-grained stripe size always equals
128 KB; this provides lower I/O latency for small I/O
operations such as redo log writes."
It appears that coarse-grained striping
and fine-grained striping are done automatically at ASM file
"Coarse-grained striping provides load
balancing for disk groups while fine-grained striping
reduces latency for certain file types by spreading the load
To stripe data, Oracle ASM separates
files into stripes and spreads data evenly across all of the
disks in a disk group.
- The coarse-grained stripe
size is always equal to the AU size (not the data extent
- The fine-grained stripe size always equals
128 KB in any configuration; this provides lower I/O latency
for small I/O operations such as redo log writes."
- "Starting in version 11gR2 Grid
Infrastructure, Oracle changed the default striping method
for ONLINELOG from fine to coarse. . . . The performance of
redo writes are much better with fine-grained striping, 7%
for a busy system and write latency improvements around 12%.
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