[Discuss] Backing up LVM partitions using snapshots

[markw at mohawksoft.com (Mark Woodward)]

In your example, a duplicate reducing backup would ignore most of the changes. 


Edward Ned Harvey <blu at nedharvey.com> wrote:

>> From: markw at mohawksoft.com [mailto:markw at mohawksoft.com]
>> Sent: Sunday, December 11, 2011 2:48 PM
>> 
>> I will argue that an rsync will NEVER be more effective unless you
>> actively wipe the blocks where a file once existed. 
>
>for (( i=0 ; i<200 ; i++ )) ; do
>mkdir temp
>cp datafile temp
>run_test $i >> testresults.txt
>rm -rf temp
>done
>
>In this case, rsync is what you want, because it ignores files that don't
>exist.  But a block level backup will backup all the blocks that were ever
>contained in any of the (now removed) copies of the datafile.
>
>I don't know what users you support, but I support engineers who run this
>type of test all the time.  They create test work dirs, they perform
>volatile work in there, store the results of the test, and remove their
>scratch dir.
>
>The block level backup you're talking about is great, under the assumption
>that you basically just add data to a filesystem.  It's terrible when you
>add & remove data from the filesystem.  I stand by my claim:  Important to
>know if it's suitable for your purposes, whoever you are, the consumer who
>might consider using this.
>