Text 166, 70 rader
Skriven 2006-06-19 19:47:12 av Peter Knapper (3:772/1.10)
    Kommentar till text 162 av Mike Luther (1:117/3001.0)
Ärende: File mirroring in OS/2
==============================
Hi Mike,

 ML> A while back I think mention was made of what I 
 ML> envision is a little used capability of OS/2 to 
 ML> maintain a mirror image file of a file elsewhere in the 
 ML> 'system'.  Would someone here be able to point me in 
 ML> the right direction to enable this for study?

Are you talking about the "Replication" facility available with OS/2 Peer
Networking? If so read on, otherwise forget this reply.......;-)

Be warned that Replication is NOT Mirroring of drives, but it works fine for me
and will even do so over a WAN, as long as a few basic issues are remembered.
The Replication of Data has a latency that can be configured to a small extent,
but you are still talking about an interval of up to about 5 minutes or more,
the timing of events is not under direct user control.

 ML> Does this have to be on the main OS/2 installation, say 
 ML> a mirror of a file which is in a different directory, 
 ML> on a different partition?  Or can this be on a separate 
 ML> box across an OS/2 LAN?  

Replication uses OS/2 Peer Services at either end, so it spans whatever
resources a System can access and whatever transport exists between those
sites. Effectively it works at the Drive Letter level but can be finely
controlled to only operate on a specific subdirectly structure (leaving out
parts of that if neeed) and yes, that Driver letter can be a share of a 3rd
machine.........;-)

It obviously works best on a local LAN, however to Route it over a WAN link
requires an operational IP environment, and then either TCPBEUI (and all the
security issues around that), or encapsulate the lot in a VPN.

 ML> And if the target hardware operation which is to host 
 ML> the mirrored file goes down for whatever time, then 
 ML> when it comes back up does it automagically then go 
 ML> about the busy task of updating the mirror automagically?

With Replication you set up an EXPORTER and an IMPORTER, so its a one way
environment, however you can have one machine both IMPORTing and EXPORTing at
the same time, even between the same hosts. You only need to ensure you don't
create a "ring" sharing the same data areas...

The only negative thing I have found is that you can only EXPORT from ONE Drive
letter per machine and import to ONE drive letter per machine. You can work
around this to some extent by using TVFS but there is an overhead in doing
that.

 ML> Such that I could thus 'mirror' all the critcal data files on a mission 
 ML> critical discrete OS/2 system, off site, without the 
 ML> use of backup techniques such as tape or disk cloning?  

Yes, it works great, as long as you handle a few potential "issues"
apprpriately........;-)

 ML> Thus not having to take the critical system off-line to 
 ML> do the backup.  

This may be the show stopper, as it can ONLY operate on CLOSED files.
Replication sets hooks into the OS so IT is notified when a file is CLOSED. The
SOURCE file MUST be closed by ALL applications before it can be replicated, an
always open DB will NEVER be replicated.

If you need more info I can send some docs I wrote up about Replication.

Cheers.............pk.


--- Maximus/2 3.01
 * Origin: Another Good Point About OS/2 (3:772/1.10)