[Linux-cluster] Cluster with shared storage on low budget

[yvette hirth]

Thomas Sjolshagen wrote:

> Just so you realize; If you intend to use clvm (i.e. lvme in a cluster 
> where you expect to be able to write to the volume from more than one 
> node at/around the same time w/o a full-on failover), you will _not_ 
> have snapshot support. And no, this isn't "not supported" as in "nobody 
> to call if you encounter a problem", it's "not supported" as in "the 
> tools will not let you create a snapshot of the LV".

i've been listening to this discussion with much interest, as we would 
like to improve the currency of our backup files.

right now we have an ensemble of GFS2 LV's ("pri") as our primary data 
store, and a "matching ensemble" of XFS LV's ("bak") as our backup data 
store.  an hourly cron job rsync's all LV's in the ensemble from pri => 
bak.  it's incredibly reliable, but this reduces our mean backup 
currency by 1/2 hour.  one upside is that i've got snapshots that are 
only 1/2 hour old, and are daily backed up to tape.

the conversation seems to indicate that we can change the bak LV's from 
XFS to GFS2 and have drbd auto-sync the pri LV changes made to the bak 
LV's - yes?  this would reduce our backup currency from a mean of 1/2 
hour to theoretically, "atomic" (more likely "mere seconds").  i assUme 
we have to change from XFS to GFS2, as drbd doesn't appear to do file 
system conversions...

if our assumptions are correct, are there any guides / manuals / doc on 
how to do this?  it's most tempting to try, since if it doesn't work, 
the hourly cron rsync's could be simply reinstated.

many thanks in advance to any and all who can advise...

yvette