UTSL. compressratio is the ratio of uncompressed bytes to compressed bytes. http://cvs.opensolaris.org/source/search?q=ZFS_PROP_COMPRESSRATIO&defs=&refs=&path=zfs&hist=&project=%2Fonnv
IMHO, you will (almost) never get the same number looking at bytes as you get from counting blocks. -- richard Stuart Anderson wrote: > On Mon, Apr 14, 2008 at 05:22:03PM -0400, Luke Scharf wrote: > >> Stuart Anderson wrote: >> >>> On Mon, Apr 14, 2008 at 09:59:48AM -0400, Luke Scharf wrote: >>> >>> >>>> Stuart Anderson wrote: >>>> >>>> >>>>> As an artificial test, I created a filesystem with compression enabled >>>>> and ran "mkfile 1g" and the reported compressratio for that filesystem >>>>> is 1.00x even though this 1GB file only uses only 1kB. >>>>> >>>>> >>>>> >>>> ZFS seems to treat files filled with zeroes as sparse files, regardless >>>> of whether or not compression is enabled. Try "dd if=/dev/urandom >>>> of=1g.dat bs=1024 count=1048576" to create a file that won't exhibit >>>> this behavior. Creating this file is a lot slower than writing zeroes >>>> (mostly due to the speed of the urandom device), but ZFS won't treat it >>>> like a sparse file, and it won't compress very well either. >>>> >>>> >>> However, I am still trying to reconcile the compression ratio as >>> reported by compressratio vs the ratio of file sizes to disk blocks >>> used (whether or not ZFS is creating sparse files). >>> >>> >> Can you describe the data you're storing a bit? Any big disk images? >> >> > > Understanding the "mkfile" case would be a start, but the initial filesystem > that started my confusion is one that has a number of ~50GByte mysql database > files as well as a number of application code files. > > Here is another simple test to avoid any confusion/bugs related to NULL > character sequeneces being compressed to nothing versus being treated > as sparse files. In particular, a 2GByte file full of the output of > /bin/yes: > > >> zfs create export-cit/compress >> cd /export/compress >> /bin/df -k . >> > Filesystem kbytes used avail capacity Mounted on > export-cit/compress 1704858624 55 1261199742 1% /export/compress > >> zfs get compression export-cit/compress >> > NAME PROPERTY VALUE SOURCE > export-cit/compress compression on inherited from > export-cit > >> /bin/yes | head -1073741824 > yes.dat >> /bin/ls -ls yes.dat >> > 185017 -rw-r--r-- 1 root root 2147483648 Apr 14 15:31 yes.dat > >> /bin/df -k . >> > Filesystem kbytes used avail capacity Mounted on > export-cit/compress 1704858624 92563 1261107232 1% /export/compress > >> zfs get compressratio export-cit/compress >> > NAME PROPERTY VALUE SOURCE > export-cit/compress compressratio 28.39x - > > So compressratio reports 28.39, but the ratio of file size to used disk for > the only regular file on this filesystem, i.e., excluding the initial 55kB > allocated for the "empty" filesystem is: > > 2147483648 / (185017 * 512) = 22.67 > > > Calculated another way from "zfs list" for the entire filesystem: > > >> zfs list /export/compress >> > NAME USED AVAIL REFER MOUNTPOINT > export-cit/compress 90.4M 1.17T 90.4M /export/compress > > is 2GB/90.4M = 2048 / 90.4 = 22.65 > > > That still leaves me puzzled what the precise definition of compressratio is? > > > Thanks. > > --- > Stuart Anderson [EMAIL PROTECTED] > http://www.ligo.caltech.edu/~anderson > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
