Date: Sun, 21 Feb 2010 01:50:26 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Aiza <aiza21@comclark.com> Cc: freebsd-questions <questions@freebsd.org> Subject: Re: Dump questions Message-ID: <20100221075026.GL70798@dan.emsphone.com> In-Reply-To: <4B80E4AF.3040204@comclark.com> References: <4B80ABBA.9000707@comclark.com> <20100221061449.GK70798@dan.emsphone.com> <4B80E4AF.3040204@comclark.com>
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In the last episode (Feb 21), Aiza said: > Dan Nelson wrote: > > In the last episode (Feb 21), Aiza said: > >> 1. Using the -L flag to create a snapshot of the live running file > >> system. > >> > >> Does this mean that a complete copy of the file system is written to > >> .snap directory? > > > > No; that would be a "copy". Snapshots only copy blocks as they are > > modified on the parent filesystem, so their size is determined by how > > much data is modified since the snapshot was created. > > So how does this interact with the dump process? > > Dump start reading and writing its dump file and as the live system > changes the changes are written to the .snap and when dump completes it > overwrites it dump with the changes from the .snap??? > > How does this process work in detail? Dump reads from the snapshot, which is guaranteed not to change while dump is running. When its done, dump deletes the snapshot file. Changes made after the dump has started will not be saved. This is the same as any other backup system that uses snapshots afaik; none try and catch up changes made while the backup itself is running. You could run another incremental dump right after the previous one, which would back up any changes since the first one. -- Dan Nelson dnelson@allantgroup.com
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