You don't menotion what Version/Release the system runs so I'll assume it's
V7R3 or V7R4.

I'm guessing you are referring to 5770SS1, option 42, HA Journal
Performance. Use GO LICPGM, then option 10 to see if it is loaded. If
not, end of query. if it is then WRKLICINF and see if there is a license
attached to it. If not it's not licensed, therefore not being used.

That product is designed for application replication packages (iCluster,
Mimix, and the like) that use journals to push the data across. In your
case the SAN is doing all that work for you so my guess is you don't have a
concern. The lag time between production and the HA side will be highly
dependent on the speed of the line between the two, but it's usually
several milliseconds assuming everything is set up correctly and the
LAN/WAN does not build in latency.

Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects

On Fri, Nov 19, 2021 at 6:42 PM Laurence Chiu <lchiu7@xxxxxxxxx> wrote:

We are about to go live with a system with two Power servers both running
IBM FlashSystes V5030 SANs fully populated with SSDs.

We are utilising Metro Mirror to keep our production and DR SANs in sync so
if production dies we can make our remote SAN LUN as writeable and IPL the
DR box.

Somebody mentioned to me be wary of journal caching turned on with the
command JRNCACHE(*YES) function in CHGJRN as you could have uncommitted
journals around when the system crashed and thus lose data. Another piece
of advice said you might only lose a few milliseconds of data in a worst
case sceario.

Given we don't have a high transaction volume system and the SANs are very
fast, it seems we could turn that feature off and not lose any performance
and also not lose any data. Does that seem like a reasonable option to
explore? Also it appears that journal caching is a paid option and since
this application is quite old and the configuration is not that well
documented, is there an easy way to tell if that option has been purchased
and is turned on?

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