[Lustre-discuss] MDT backup

[Alex Kulyavtsev]

Hi,
what is the right way to backup MDT ? People get worried what will  be 
"The Day After" the catastrophic disk failure.
We are about to release lustre system into production, preproduction 
testing went good so far (Thanks !).

- At present we do LVM snapshots to backup MDT and we were able to 
restore snapshot to another node.
Is there any way to capture changes made on MDT after snapshot done and 
how close can we get to point of crash ? Is there some kind of MDT 
journal synchronized with LVM snapshot ? Is there way to do incremental 
backups to do it more often ?

- What is an experience with DRBD replication ? There are multiple 
reports from sites using it and there are also there are reports 
indicating replicated file system is not clean when master MDT crashes 
as DRBD knows nothing and does not synchronize with file system on top 
of it.
Is there way to avoid corruption or it just fixed by fsck ? Can DRBD 
failover "cleanly" if we do it manually e.g. to upgrade master MDS ?
Can I verify slave disk is consistent with master and is not corrupt 
after a year of running ?

It seems like both LVM and DRBD approaches are not perfect. Are there 
plans to implement native replication of MDT in lustre ?
SNS is for OSTs only, right ?

I would appreciate to hear about experience on MDT backup.

Thanks, Alex.