Date: Sun, 18 Jan 2004 23:11:51 -0500 From: Jesse Guardiani <jesse@wingnet.net> To: freebsd-current@freebsd.org Subject: filesystem snapshot question Message-ID: <bufle7$bsb$1@sea.gmane.org>
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Howdy list, I've read some of the documentation written about the new filesystem snapshot feature in 5.x, and I've used it a few times on my laptop. Very very slick. However, I can't seem to find a good explanation of exactly HOW it works and what performance issues are involved. Snapshots don't seem to take up much disk space. (even though `ls -al` will report that the snapshot is as large as the slice on which it resides at the time the snapshot was created) So when a snapshot is active on a filesystem, does every disk write happen twice? Once to the real filesystem and once to the snapshot with old data? I mean, it CAN'T actually be making a copy of the filesystem. :) My disk doesn't have enough free space. Is there a way to actually figure out how much data the snapshot has allocated at any given time? Does a snapshot physically grow on the disk as changes are made to the real filesystem? Just hoping to understand things better. Thanks! -- Jesse Guardiani, Systems Administrator WingNET Internet Services, P.O. Box 2605 // Cleveland, TN 37320-2605 423-559-LINK (v) 423-559-5145 (f) http://www.wingnet.net
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