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Forum Discussion
ReadyNAS Rync Backup
I know there is much discussion on this topic however I can't find a direct answer.. I'm attempting a backup via GUI from a 4312 and a 4360 NAS and am using the backup ui to do so. I have a pull job (rsync server not rsync serv via ssh) from the 4360 to backup the 4312 and want to also copy the snapshots directory for each share however it's skipping this Directory. I don't have it listed in "exclusions" but it is skipping anway. Is this because I'm doing a pull as opposed to a push? Thanks
6 Replies
dallis11 wrote:
and want to also copy the snapshots directory for each share however it's skipping this Directory. I don't have it listed in "exclusions" but it is skipping anway. Is this because I'm doing a pull as opposed to a push?
No. It's because trying to backup the snapshots leads to really bad results, so the system won't let you do that.
BTRFS snapshots are practical because the file system uses CoW. Each snapshot looks like it has the full file system at the time the snapshot was taken when you browse, but the on-disk space usage is incremental. If you try to copy the snapshot with rsync, SMB, etc you will end up with a full copy of the file system for each snapshot.
So if you take daily snapshots of a 500 GB share for 30 days, it would take 30*500GB (15 TB) just to back up those snapshots. Most people simply don't have the space in the backup device to handle this.
What you can do is enable custom snapshots on the destination 4360. For instance, if you run daily backups you can also take a daily snapshot (ideally timed right before the backup runs). Then you'd still be able to recover old file versions on the 4360. The snapshots won't exactly match the snapshot list that is on the source 4312, but it does give you what amounts to a versioned backup set of the 4312.
ReadyDR will copy the snapshots. The only thing with ReadyDR, though, is that you don't get a usable share on the target device, you just get snapshots. So, if you need to get access to files, you have to clone a snapshot, which does not include the snapshots before it. Those snapshots from earlier are still there in the ReadyDR target, but switching to the backup NAS in the event of disaster on the main one is not made easy by all this.
Sandshark wrote:
ReadyDR will copy the snapshots. The only thing with ReadyDR, though, is that you don't get a usable share on the target device, you just get snapshots. So, if you need to get access to files, you have to clone a snapshot, which does not include the snapshots before it. Those snapshots from earlier are still there in the ReadyDR target, but switching to the backup NAS in the event of disaster on the main one is not made easy by all this.
Yes.
Since I want a highly available backup, I don't use ReadyDR. But if you have 2x the capacity on the 4360, you could potentially do both - mirror the shares with Rsync (no snapshots in the mirror), combined with ReadyDR for snapshot backup.
Thanks for the snapshot explanation. I wasn't understanding that it is meerly block pointers to diff RAID disk sectors and not increm. data. Skipping ReadyDR as the copy RAID disk structure and slow restore would be too slow for us.
Restoring a ReadyDR backup to a useable share on the backup system is nearly instantaneous. That, too, is just setting up a new set of pointers to existing data bloack. Copying the data from that share back to the original would take the same amount of time as doing so from any other backup.
There can be other reasons to use something other than ReadyDR, but I wanted you to know you seem to have one item wrong in your evaluation.
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