Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
> I am exploring the use of DRBD as a backup system for some servers. > So far I've installed it on a couple of test servers, and it's worked > well - once I understood some idiosynchrasies of the command line :) > Hints would be helpful ;) MG: I am not quite sure if you mean "DRBD should give the user hints" or "can you tell me what's wrong" :) My biggest problem in learning DRBD was not knowing how the different tools interact - I didn't realise that /etc/init.d/drdb start would do everything. The second problem was misinterpreting the error messags - if you've already got a resource up and working, the command line tools should have errors which say "the resource is working", not "device in use" - which sounds like something is wrong! Most of this is of course newbie stuff - and no, I didn't read the manual properly ;) > - LVM seems inefficient if you add multiple snapshots > - Ext3Cow has no way of deleteing snapshots > - DRBD won't actually load on top of cowloop ... > What exactly do you mean by "LVM seems inefficient". You can set the chunksize of the snapshot when taking it... they are read/writable... I like LVM2's snapshots... MG: Well, I'm trying to create multiple historical backups - e.g. one for each day of this week and one for each of the past four weekends. My guess - and I've not been able to figure this - is that if you were to do this, LVM would need to make an additional write per active snapshot. Maybe I should do more testing of this. > This is my approach: > > - Disconnect DRDB > - Change beta to primary > - Mount it > - Make a backup > - Unmount > - Change it back to secondary > - Reconnect > > It this correct? This would produce a bad mess... Since this looks like a split brain situation to DRBD. Disconnect ; mount it in read-only mode ; reconnect MG: Hmm... this suggests you can mount the secondary RO without changing to primary? I thought I read in the source that you can't mount at all when not primary. > I tried exactly this case, copying a 100mb file, then reconnecting. I > then immediate ran cat /proc/dbrd - but it did not show sync in progress. Hmm ? As long as the "ap:" value in /proc/drbd is greater than zero there is some data in flight... MG: AH! OK, that's the bit I missed... I use DRBD on top of LVM, so I take the snapshot off the LV and do the backup... No need to disconnect it... MG: Sorry, would you mind explaining the steps in this? Sounds good though... Thanks very very much!! Martin Green