Oracle ASM hidden parameters





_disable_rebalance_compact : Setting _DISABLE_REBALANCE_COMPACT=TRUE will disable the compacting phase of the disk group rebalance.


Since version 11.1, the ASM performs a disk compacting once the rebalance is complete.
This may have a noticeable impact on the first rebalance after the upgrade from 10g.
The idea of the compacting phase it to move the data as close the outer tracks of the disks
(the lower numbered offsets) as possible. The first time the rebalance runs in 11g, it could
take a while if the disk group configuration changed – for example after an ALTER
DISKGROUP … ADD DISK. Subsequent manual rebalance without a configuration change
should not take as much time.
A disk group where the compacting phase of the rebalance has done a lot of work will tend to
have better performance than the pre-compact disk group. The data should be clustered near
the higher performing tracks of the disk, and the seek times should be shorter.
Relevant initialization parameter: _DISABLE_REBALANCE_COMPACT.
Relevant disk group attribute: _REBALANCE_COMPACT.
The holemarks of the compacting phase:

  • Rebalance is taking ‘too long’
  • Updates to gv$asm_operation have stopped
  • In the ARB0 trace file we see many lines like this: ARB0 relocating file +<diskgroup>.nnn.mmm (1 entries)
  • Stack (systemstate, processstate or pstack) shows kfdCompact() function.



If set, limit the number of full scans (of all disks) we do when reading the
PST in kfdp_readMeta(). This is also required to activate split PST checks
(which rely on the lock value block being available)



_asm_evenread – enable/disable even read.
0 = Defer to the disk group attribute (to be implemented)
1 = ENABLE (always on)
2 = DISABLE (always off)
18 = Enabled iff offline disks are found
_asm_evenread_tracing – tracing; 0 is off, 1 is 1 line per IO, 3 is verbose
_asm_evenread_alpha -alpha value, x2^14 (16 is a good value)
_asm_evenread_alpha2 – secondary alpha value, x2^14
_asm_evenread_faststart – number of IOs after offline/online to use alpha2 (default 0)






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