Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Wed, Apr 8, 2009 at 1:13 PM, Peter Sabaini <peter at sabaini.at> wrote: > On Wednesday 08 April 2009 18:38:54 you wrote: >> > A crucial factor is wether you can tolerate stale data. Running rsync >> > periodically will probably result in not-quite-uptodate replication when >> > the storm troopers come rushing in and cut your power. If that is not a >> > concern, eg. because your data doesn't change all that often, or you >> > simply don't care about a few lost updates, then rsync is IMHO simpler to >> > set up. >> > >> > In contrast, DRBD does real replication. Depending on your link/network >> > quality and the chosen protocol you can guarantee that local writes are >> > only considered complete if the remote side also has completed. >> >> Maybe it is a re-incarnation of executive order 6102, to melt down the >> servers for their gold content? >> >> Anyhow, provided the bandwidth is sufficient, I prefer the DRBD >> option. However, will the backups be successful, if the backup drive >> is attached to the secondary? Most of what I've read suggests that >> you shouldn't even mount the secondary in read-only mode (although >> maybe an LVM snapshot can be mounted for taking a backup). > > DRBD won't allow you to mount a secondary. This means you either have to use a > Dual Primary setup (requiring a cluster filesystem) or make a block-level > backup (don't know if thats adivsable). Maybe you can temporarily disconnect > DRBD for the backup, promote the secondary, mount + backup, demote again, and > reconnect -- Im not really sure if this would work though, you'd have to try. > > peter. I also don't think a snapshot will work either. The first step in creating a snapshot is to quiesce every thing, then create the snapshot. Since the quiesce would have to happen on the primary, I don't think you could properly coordinate a snapshot being created on the secondary. If tape is critical to your situation, you may need to stick to rsync. FYI: I think this should be added to the drdb wishlist. I think some commercial SAN devices that replicate have to ability to mount the remote copy by using snapshot technology on the remote. And I know some support what Peter describes which is effectively: quiesce primary stop block transmissions from primary to secondary mount secondary in read-only form perform backup unmount secondary release drdb to continue updates If drdb doesn't support that, I'd also like it to go on the wishlist. Thanks Greg -- Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com