re: INFORMIX disk mirroring across LANs

Al Parker writes, > What I would like to achieve is disk-mirroring from one system to another. > From what I can see, the disk-mirroring abilities of INFORMIX ON-LINE 4.0 > (which we are using :') will not support mirroring databases to remote > systems. Indeed. We should probably be grateful that it isn't supported. Ask yourself this question: If INFORMIX On-Line is expecting to be able, at all times, to mirror to the remote database (or drive), and that database (or drive) becomes suddenly unavailable due to the failure of a communications link (as often happens), what is going to happen to your On-Line session? If the theoretical link to a remote database is designed to be fault-tolerant, okay; all that will happen is that the data won't get mirrored for awhile. But then what happens? The On-Line engine would have to keep doing some kind of net queries to ask if the remote database is available until it becomes active again ("Are you there?" << no answer>> "Are you there?", etc.). This will slow down your On-Line session from the outset. Then, when the remote database becomes available again, just picking up with mirroring transactions from wherever you happen to be won't be good enough - On-Line will have to check the status of the remote database, then bring it "up to speed" with the active database: another monumental loss of time, if you have a busy database. From a performance standpoint, I hope this "feature" is not implemented - everyone and their cousin who uses that feature is going to scream blue bloody murder, when they have a LAN failure and a busy database. Again, from a performance standpoint, your best bet is to use raw devices and mirror to a second physical drive - preferably one NOT on the same SCSI controller. Hope this helps. Bill Williams ------------------------------------------------------------------------------ STANDARD DISCLAIMER: Any opinions offered by me are mine alone and in no way reflect the judgment or opinions of the US Air Force, Department of Defense, or United States Government. BUT THEY SHOULD! ------------------------------------------------------------------------------