Using rsync for buidling Oracle standbys.

[Matt McCutchen]

On Thu, 2009-09-03 at 10:25 -0700, Saibabu Devabhaktuni wrote:
> We currently use rsync to create an Oracle standby on a target box
> from an existing standby by copying all the datafiles while the source
> standby is in recovery status. We are occasionally running into
> datafile corruptions being reported by oracle when it is recovering
> the new standby. Oracle support says they don't recommend copying
> files while the changes being applied to them unless the database is
> put in backup mode (which is not possible for us).
> 
> We are using "rsync -av --password-file=pass.secret
> source_data_file_name oracle at target::ORCL/"
> 
> We are planning to use "rsync -av --password-file=pass.secret
> --block-size=8192 source_data_file_name oracle at target::ORCL/"
> 
> This is because, we are using 8k block size for Oracle and hence the
> blocks will be copied in full by rsync to avoid fractured block
> copies. Am I correct in this assumption by using "--block-size"
> option?

No.  --block-size sets the block size for the delta-transfer algorithm;
rsync does not provide a way to set the size of its read(2) calls.  And
even if it did, it would appear from the following message that read(2)
calls are not atomic on Linux:

http://marc.info/?l=linux-kernel&m=107375454908544

I would recommend looking into a block-device-level snapshot facility
such as LVM snapshots.

(Note: a similar issue was discussed in this thread:

http://lists.samba.org/archive/rsync/2009-May/023270.html

but the non-atomicity of read(2) calls was not considered.)

-- 
Matt