Tino Schwarze wrote at about 12:20:50 +0100 on Friday, October 31, 2008: > On Thu, Oct 30, 2008 at 11:16:05PM -0400, Jeffrey J. Kosowsky wrote: > > > I must be missing something on this whole compression, pooling, and > > checksum matter. > > > > I found 2 files in my cpool that have the same checksum (one is _0) > > but 'cmp' to different values. However, when I zcat them, they have > > the same value. I thought that (lossless) compression was a 1-1 > > mapping? > > Please post the output of the following: > ls -l yourfile* > md5sum yourfile* > BackupPC_zcat yourfile | md5sum > BackupPC_zcat yourfile_0 | md5sum
-rw-r----- 5 backuppc backuppc 7870 Oct 27 16:28 /var/lib/BackupPC/cpool/5/f/8/5f87fe62e8254679c582097314f97fe3 -rw-r--r-- 2 backuppc backuppc 7681 Oct 28 09:17 /var/lib/BackupPC/cpool/5/f/8/5f87fe62e8254679c582097314f97fe3_1 08be9e936c80024809fde108f6df9bb1 /var/lib/BackupPC/cpool/5/f/8/5f87fe62e8254679c582097314f97fe3 ce46e80af4a086e29ae17b0f800362e1 /var/lib/BackupPC/cpool/5/f/8/5f87fe62e8254679c582097314f97fe3_1 4266be808f85826aedf3c64c1e240203 4266be808f85826aedf3c64c1e240203 > > > But here we seem to have two files that are identical (and thus have > > the same checksum) but compress to 2 *different* results? > > Again: The file name ist NOT the checksum of the whole file's contents! > It's just an MD5 sum which incorporates the first 256k of the file and > the file's original length (as I learned this week from this list). Yes but this is the OPPOSITE of hash collisions. Hash collision is when 2 *different* (uncompressed) files have the *same* checksum. Here 2 *identical* (uncompressed) files have *different* checksums. As Craig and Holger explained, this is probably also attributable to corruption where some backups had the rsync caching seeds included an others not. > > > This would seem to be going against the grain of pooling where two > > identical files share the same pool entry. > > > > What am I missing? > > That hash collisions are expected. Yes but that is not the case here. > > Tino. > > -- > "What we nourish flourishes." - "Was wir nähren erblüht." > > www.lichtkreis-chemnitz.de > www.craniosacralzentrum.de > > ------------------------------------------------------------------------- > This SF.Net email is sponsored by the Moblin Your Move Developer's challenge > Build the coolest Linux based applications with Moblin SDK & win great prizes > Grand prize is a trip for two to an Open Source event anywhere in the world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > BackupPC-users mailing list > BackupPC-users@lists.sourceforge.net > List: https://lists.sourceforge.net/lists/listinfo/backuppc-users > Wiki: http://backuppc.wiki.sourceforge.net > Project: http://backuppc.sourceforge.net/ ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ BackupPC-users mailing list BackupPC-users@lists.sourceforge.net List: https://lists.sourceforge.net/lists/listinfo/backuppc-users Wiki: http://backuppc.wiki.sourceforge.net Project: http://backuppc.sourceforge.net/
