Notes:
ahead queue. Likewise rat should not exceed raq because only raq tracks or block groups can be
queued at any time.
This is because one writer thread could be CPU-bound (compressing a track or block-group
image) and the other could be i/o-bound (writing the compressed image).
group image will reside in storage before being written to the emulation file. A large value may
mean more data loss if a catastrophic error occurs. A small value may mean that more CPU time
is spent compressing images.
For example, suppose that a particular image is updated several times each second. If the inter-
val is changed from the default 5 seconds to 1 second, then that image will be compressed and
written 5 times more frequently. A large value may cause more cache flushes within a garbage
collection interval. These kinds of flushes mean that a read will wait because there are no avail-
able cache entries, slowing the emulated operating system. A large value will also cause more
pending free space to build up (since free space is flushed each interval). This may mean that the
garbage collector space recovery routine will perform more work and the resulting emulation file
may be larger.
failure. fsync will ensure your data on disk is coherent. However, fsync may cause a noticeable
performance degradation. Note that an fsync will not be performed more often than every 5
seconds.
5.10.4 Examples
Example 1:
Set the CCKD options to use bzip2 as compression method and using maximum compression.
CCKD COMP=2,COMPPARM=9
Example 2:
Set the CCKD options to use the default compression method, as well as default compression. Disable
stressed writes and set the number of trace entries to 100000.
CCKD COMP=-1,COMPPARM=-1,NOSTRESS=1,TRACE=100000