Date: Thu, 20 Oct 2005 11:01:42 -0400 (EDT) From: user <user@dhp.com> To: freebsd-questions@freebsd.org Subject: FreeBSD UFS2 snapshots, and math ... Message-ID: <Pine.LNX.4.21.0510201101260.31267-100000@shell.dhp.com>
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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.
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