Disaster Recovery and Rsync (was [lug] Commercial rsync service?)

[Nate Duehr]

Jeffrey Siegal wrote:

>> (3) How do databases work? Do you have to stop the (for example) MySQL
>> deamon while you do the rsync? My guess is definitely. What about the
>> subversion or cvs deamons? Could this be a problem if you try to use a
>> single rsync command for an entire computer's local storage and it 
>> takes a
>> long time? It seems to me like you would want to have a lot of short 
>> shell
>> scripts to run daily so you don't have to shut down all your servers 
>> at once
>> for the entire duration of the synchronization.
> 
> One way do deal with this is to use LVM snapshots.  Snapshot, mount 
> snapshot read only, rsync from snapshot, unmount and then delete the 
> snapshot.

This is very common in the commercial world.  There's another step 
usually...

Put DB in quiet mode. (No disk reads or writes, but DB is still up.)
snapshot
Put DB back in normal mode.

Then the rest, as you mentioned.

I worked on a system where they spooled off a DB snapshot to a tape 
carousel every weekend this way... big database... took about 10 AIT-3 
tapes, just for the main stuff out of it, if I remember correctly.

Not the biggest I've ever worked on, but AIT-3 was pretty fast and it 
still took a very long time every weekend.

Nate