Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964956AbXABTfQ (ORCPT ); Tue, 2 Jan 2007 14:35:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964959AbXABTfP (ORCPT ); Tue, 2 Jan 2007 14:35:15 -0500 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:4761 "EHLO spitz.ucw.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S964955AbXABTfN (ORCPT ); Tue, 2 Jan 2007 14:35:13 -0500 Date: Tue, 2 Jan 2007 19:15:05 +0000 From: Pavel Machek To: Miklos Szeredi Cc: bhalevy@panasas.com, arjan@infradead.org, mikulas@artax.karlin.mff.cuni.cz, jaharkes@cs.cmu.edu, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, nfsv4@ietf.org Subject: Re: Finding hardlinks Message-ID: <20070102191504.GA5276@ucw.cz> References: <20061221185850.GA16807@delft.aura.cs.cmu.edu> <1166869106.3281.587.camel@laptopd505.fenrus.org> <4593890C.8030207@panasas.com> <1167300352.3281.4183.camel@laptopd505.fenrus.org> <4593E1B7.6080408@panasas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1313 Lines: 37 Hi! > > >> It seems like the posix idea of unique doesn't > > >> hold water for modern file systems > > > > > > are you really sure? > > > > Well Jan's example was of Coda that uses 128-bit internal file ids. > > > > > and if so, why don't we fix *THAT* instead > > > > Hmm, sometimes you can't fix the world, especially if the filesystem > > is exported over NFS and has a problem with fitting its file IDs uniquely > > into a 64-bit identifier. > > Note, it's pretty easy to fit _anything_ into a 64-bit identifier with > the use of a good hash function. The chance of an accidental > collision is infinitesimally small. For a set of > > 100 files: 0.00000000000003% > 1,000,000 files: 0.000003% I do not think we want to play with probability like this. I mean... imagine 4G files, 1KB each. That's 4TB disk space, not _completely_ unreasonable, and collision probability is going to be ~100% due to birthday paradox. You'll still want to back up your 4TB server... Pavel -- Thanks for all the (sleeping) penguins. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/