From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oystein Viggen Subject: Re: What do the arguments of btrfs filesystem defragment do? Date: Thu, 16 Dec 2010 09:41:50 +0100 Message-ID: <037hfaxg6p.fsf@msgid.viggen.net> References: <4D08E76B.40400@logtenberg.eu> <1292439708-sup-2951@think> <4D091387.9050905@logtenberg.eu> <1292440771-sup-9278@think> <4D091679.80706@logtenberg.eu> <1292441925-sup-1105@think> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 To: linux-btrfs@vger.kernel.org Return-path: List-ID: * [Chris Mason]=20 > Excerpts from Erik Logtenberg's message of 2010-12-15 14:26:49 -0500: >>=20 >> The use case is a filesystem used for backups, which are rsynced >> nightly, after which a new snapshot is made. After something like 45 >> days, the old snapshots are removed. I am assuming that this way, af= ter >> 45 days all files will be compressed naturally, but this is only >> beneficial if snapshots still fully work. If instead it results in >> storing the compressed form of every file 45 times on disk, then it >> won't help much. > > Yes, you'll end up with a fully compressed and fully shared setup aft= er > 45 days. How would that happen? Rsync only rewrites files if they have changed. If compression happens only when a file is written to, any files that were written uncompressed will remain uncompressed until they change on the source filesystem (triggering a rewrite on the backup drive). Unless there's some magic I'm missing, expiring the old snapshots from before -o compress won't really affect anything. =D8ystein --=20 Outgoing mail is certified Virus Free. =2E.of course, the virus would tell you the same thing.. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html