zfs discuss - Jan 2006 - Compression and then some?

I was somewhat surprised at the following behavious of zfs; I created
three files, one all random, one all "x" and the 3rd one all zeros.

Does this mean that zfs compression makes holes in files (as there''s
1 block of "meta data" associated with the file)

$ ls -ls zeros xes random
 129 -rw-------   1 casper   ir         65536 Jan 26 16:12 random
   6 -rw-------   1 casper   ir         65536 Jan 26 16:11 xes
   1 -rw-------   1 casper   ir         65536 Jan 26 16:11 zeros

Casper

Hello Casper,

Thursday, January 26, 2006, 4:38:32 PM, you wrote:


CDSC> I was somewhat surprised at the following behavious of zfs; I created
CDSC> three files, one all random, one all "x" and the 3rd one all
zeros.

CDSC> Does this mean that zfs compression makes holes in files (as
there''s
CDSC> 1 block of "meta data" associated with the file)

CDSC> $ ls -ls zeros xes random
CDSC>  129 -rw-------   1 casper   ir         65536 Jan 26 16:12 random
CDSC>    6 -rw-------   1 casper   ir         65536 Jan 26 16:11 xes
CDSC>    1 -rw-------   1 casper   ir         65536 Jan 26 16:11 zeros

If you got compression=on and a block is all 0s then no actual
compression occurs and only meta are updated (not even block is
allocated).

http://milek.blogspot.com/2005/12/writing-zeros-to-zfs-files.html



-- 
Best regards,
 Robert                            mailto:rmilkowski at task.gda.pl
                                   http://milek.blogspot.com