On 25 May 2007 07:15:18 -0700, in bit.listserv.ibm-main
(Message-ID:<[EMAIL PROTECTED]>)
[EMAIL PROTECTED] wrote:
In a message dated 5/25/2007 8:23:00 A.M. Central Daylight
Time,
[EMAIL PROTECTED] writes:
Depending on your actual spinning DASD, compression may
be counter
productive for actual disk utilization. It can save
logical space and
cache space but if the controller is compressing the data
in cache to
store it on disk, this may foul up the compression
algorithm.
<snip>
How can compressing the data in cache foul up
the algorithm?
On my PC, I have a DAT drive for backup which does
hardware compression. It holds 2GB, native capacity on a
tape. If I back up a file which doesn't compress, it holds
only about 1.8GB unless I turn off compression. (At first
I thought I had short media; now I turn off hardware
compression for 2GB already-compressed files.)
If you zip a zipped file, you will usually end up
with a somewhat larger file.
In almost all cases that I know of, attempting to
compress a compressed file will take extra time and
space. I think that Clark Morris's statement that
compressing "may foul up the compression algorithm" did not
mean that the algorithm wouldn't work, but that it might
yield non-optimal results.
--
I cannot receive mail at the address this was sent from.
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