I have a server running Citadel which uses Berkeley DB on the back end
and I am trying to transfer the VM that is running it to a different
server and when I just copy the virtual hard drive and load it the
database is corrupt and cannot be fixed. When I try anything else like
db_hotbackup I get an input/output error when it tries to backup the
logs. The host system is running Fedora 16 and the VM is running Centos
6.3 Using qemu and KVM for the virtualization. I really have 2 questions.

1. How long should it take to dump a database? Mine is about 7.4 GB with
about 200 MB of log files right now.

2. What is the best way to transfer the database to a different system?
I would prefer a method that does not involve downtime as this is a
production email system.

* jeff:

This is odd. Are you copying a volume which is being written to? If
you copy a read-only snapshot, it should work.

That mostly depends on fragmentation. About an hour would not be
entirely unheard of.

You need to make the database read-only at one point, otherwise some
writes will be lost. And if you change versions of Berkeley DB, you
have to perform environment recovery, which also requires downtime.

On 08/10/2012 11:34 AM, Florian Weimer wrote:
Yes it is being written to right now because it is production. I will
see about scheduling some downtime for this.

Only an hour, that is not a problem but the dumps that I have attempted
have taken 8-10 hours and either never finished or came up with an error.

I have reason to believe that I am pushing the limits of the hard drive
IO even though the drives I am using are not exactly slow, but the
results of trying to copy does not seem to be effected by other virtual
machines running on that system. From other tests that I have done I
have verified that memory, and CPU are not being used much at all, but
the IO on the hard drive, mostly waiting for random seeks might be
causing problems. I have also noticed what appears to be some possible
corruption with other VMs which from what I can tell is affected by the
drive IO since moving to the new system with a larger RAID array seems
to have fixed the problems.

* jeff:

Yes, Berkeley DB has a known bug which causes horrendous file system
fragmentation in its database files. Reading them sequentially is
very, very slow, even on beefy disk arrays.