From owner-freebsd-questions@FreeBSD.ORG Thu Oct 20 15:01:43 2005 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id DB12316A41F for ; Thu, 20 Oct 2005 15:01:43 +0000 (GMT) (envelope-from user@dhp.com) Received: from shell.dhp.com (shell.dhp.com [199.245.105.1]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9BA6943D66 for ; Thu, 20 Oct 2005 15:01:43 +0000 (GMT) (envelope-from user@dhp.com) Received: by shell.dhp.com (Postfix, from userid 896) id 8430C312FD; Thu, 20 Oct 2005 11:01:42 -0400 (EDT) Date: Thu, 20 Oct 2005 11:01:42 -0400 (EDT) From: user To: freebsd-questions@freebsd.org Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Subject: FreeBSD UFS2 snapshots, and math ... X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Oct 2005 15:01:44 -0000 I am trying to budget some disk space for filesystems with snapshots enabled on them. The following is simplified - I am just trying to get my concepts in order: Let's say I have a filesystem, and on that filesystem I create a snapshot every single night, and every night I delete the snapshot from 5 nights ago. This means that at all times, I have four snapshots running on that filesystem, one from 1 day ago, one from 2 days ago, one from 3 days ago, and one from 4 days ago. Let's also assume that the percent change of the filesystem is 5% (every day 5% of the blocks in the filesystem are either changed or deleted). ---- Does this mean that if that 5% change is a different 5% every day, that the one day ago snapshot will be size 5%_of_filesystem, and that the 2 day ago snapshot will be size 10%_of_filesystem, day 3 15% and day 4 20%, for a total of 50% of the total filesystem taken up with snapshot data ? Does that sound correct ? When I say that the 5% change is a different 5% every day, what I mean is that it is not the same files/data being altered every day, but rather there is 5% of new data changed every day, relative to the previous nights snapshot. The second question is this: If the 5% data changed per day is the _same_ 5% every day (perhaps changing the same table in a DB every day, or perhaps changing the same block of lines in a text file every day) does that mean that every day simply represents 5%_of_filesystem, for a total of 20% of the total filesystem in use at all times for snapshot data ? ----- Finally, are there any snapshot diag tools at all ? Like, something that reports snapshot sizes, percent of disk used for snapshots, and maybe even a way for me to actually calculate what the percent change for time period X is for a particular filsystem >? Thank you.