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From "Takenori Sato(Cloudian)" <ts...@cloudian.com>
Subject Re: questions related to the SSTable file
Date Wed, 18 Sep 2013 01:19:51 GMT
Thanks, Rob, for clarifying!

- Takenori

(2013/09/18 10:01), Robert Coli wrote:
> On Tue, Sep 17, 2013 at 5:46 PM, Takenori Sato <tsato@cloudian.com 
> <mailto:tsato@cloudian.com>> wrote:
>
>     > So in fact, incremental backup of Cassandra is just hard link
>     all the new SSTable files being generated during the incremental
>     backup period. It could contain any data, not just the data being
>     update/insert/delete in this period, correct?
>
>     Correct.
>
>     But over time, some old enough SSTable files are usually shared
>     across multiple snapshots.
>
>
> To be clear, "incremental backup" feature backs up the data being 
> modified in that period, because it writes only those files to the 
> incremental backup dir as hard links, between full snapshots.
>
> http://www.datastax.com/docs/1.0/operations/backup_restore
> "
> When incremental backups are enabled (disabled by default), Cassandra 
> hard-links each flushed SSTable to a backups directory under the 
> keyspace data directory. This allows you to store backups offsite 
> without transferring entire snapshots. Also, incremental backups 
> combine with snapshots to provide a dependable, up-to-date backup 
> mechanism.
> "
>
> What Takenori is referring to is that a full snapshot is in some ways 
> an "incremental backup" because it shares hard linked SSTables with 
> other snapshots.
>
> =Rob


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