Hiya,
We have a classic enterprise-type backup setup - a number of "clients" backing
up across the network to a tape library attached to a dedicated backup host.
This is the easy bit, and works quite happily.
The tape library is an IBM TS3310 30-tape, 2-drive unit, "attached" to the
backup host via the SAN fabric.
The problem I have is with our large (expected to grow to several terabytes)
database server. I'm told by the DBAs that the size and amount of activity on
this database is such that putting the whole database into hot backup mode for
the several hours it takes to back it up is a Bad Idea, it generates far too
many log(?) files. The method they recommend is to put a single tablespace into
backup mode, back that up, put it back to normal, repeat for each tablespace.
The backup takes the same time, but doesn't generate anything like the amount
of log(?) files.
Trouble is, I can't work out how to do that with Bacula without creating a
backup job for every tablespace, which is a bit ugly because the tablespaces
change frequently and without warning, and if we have to change the Bacula
config every time it'd be too easy to miss one and thereby invalidate our
backups. Not to mention the amount of work involved.
One way I can think to do it is if I can dive into Bacula and get hold of the
"back up this file" program, and write a little script to do the database
hot-backup change, back up that file (across the network via Bacula, straight
to tape), change it back, rinse and repeat. It would need to be the Bacula
component, not something like dd or tar (did I mention these are all Linux
boxes), because it's going to be sharing a tape, in fact interleaved with, all
the other backups. Pointers, anyone?
Another way would be to abandon the Bacula tape format and present one of the
tape drives (they appear as separate WWNs on the SAN fabric) to the database
server as a dedicated drive for that host, and write in whatever format we
decide to use. The problem then is controlling the library - the changer arm is
under Bacula control for all the other hosts, so presumably the database server
would need to liaise with Bacula to nominate tapes and switch them over when
they fill up and when the backup finishes. So I'm back to the same problem as
above - digging particular functionality out of Bacula and scripting round
it... and I haven't managed to spot how to do this.
The best solution would be a combination of these two - present one of the tape
drives to the database server and have Bacula do the one-tablespace-at-a-time
routine straight to tape. This would avoid the data crossing the network,
thereby presumably speeding it up no end. But it's boggling my mind trying to
work out if it's even possible to make Bacula have a tape drive on one machine
(the db server) fed by a changer arm on another machine (the backup server).
It would be possible, I guess, to ditch the backup server and put all that
functionality on the database server. But so far I seem to have had to keep
mucking about with the backup server, rebooting it occasionally to sort out
confused tape drives (or something; not sure what's going on, but a reboot
seems to fix it), and doing that with our production database is sadly frowned
upon.
The method we're using for now is to back up the database by copying it to disk
on the backup server (via NFS), and then back that up to tape. Trouble is, this
is handling the data twice, and is currently taking well over twelve hours all
up, which given the expected growth is going to become untenable fairly soon,
so any suggestions gratefully received! Not to mention we're going to run out
of disk space!!
Help?
David.
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