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SRDF/A - SYMRDF Commands and Confusion!
I'm trying to figure out what the difference is between these two commands given the scenarios:
Scenario: DR Test (failover to DR and bring changes back when complete):
FAILOVER
a) symrdf -g failover
-or-
b) symrdf -g split
FAILBACK
a) symrdf -g failback
-or-
b) symrdf -g restore
Any insight/answers are appreciated!!!
Scenario: DR Test (failover to DR and bring changes back when complete):
FAILOVER
a) symrdf -g failover
-or-
b) symrdf -g split
FAILBACK
a) symrdf -g failback
-or-
b) symrdf -g restore
Any insight/answers are appreciated!!!
xe2sdc
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June 24th, 2008 13:00
This command will disable RW access to the R1 devices, suspend RDF replica and RW enable R2 devices. If you want to issue a failover you need to shut down hosts on the R1 side first.
This command will suspend RDF replica and RW enable both R1 and R2 devices. It's the typical command you'd issue if you want to run some tests on the R2 side while leaving production active on R1 side.
This command will disable RW access to the R2 devices and resume RDF replica from R2 toward R1 devices.. If you want to issue a failback you need to shut down hosts on the R2 side first.
This command will apply changes on the R2 side to the R1 side.
Please note that both failback and restore are incremental process, unless you use specific options.
majid7861
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June 24th, 2008 12:00
Allen Ward
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June 24th, 2008 12:00
When we run DR test we just do the split/establish to prevent anything from the DR test getting written back to the R1s. This is somewhat defined by the scope of our DR testing (we don't actually test running production in our DR environment... at least not yet).
majid7861
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June 24th, 2008 12:00
I hope this will help.
Best regards,
Majid Ali
Allen Ward
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June 24th, 2008 13:00
We even have DR tests that don't involve anything beyond calling everyone and verifying that all the contact info we have is correct to get everyone engaged.
vincent_corona
146 Posts
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June 24th, 2008 14:00
Thanks for your reply, however, I'm not sure I agree that a Split followed by a Restore is a full resync. Can you elaborate in this regard?
Additionally, when I execute a symrdf -g split, the default RDF state is "Failed over". Therefore, my only options at that point are failback, restore, or establish. Given that Establish nulls any changes at R2, I guess my main confusion is what the difference is between Failback and Restore.
Thanks!
xe2sdc
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June 24th, 2008 14:00
If you look at Symcli manuals (I'm looking at Solution Enabler 6.5 documentation CD, available here, in powerlink) you'll find so called "Composite commands" (sort of macro commands) and "Singular commands" (the building blocks).
Also note that symrdf will report a "status" that depends on various details .. It depends on the status of R1 and R2 volumes (RW, WD), the status of the link (RW, NR) and invalid tracks. If you issued a split, subsequent queries shouldn't report status as Failed Over. Can you please show the output of the commands you issued ??
majid7861
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June 25th, 2008 07:00
vincent_corona
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June 25th, 2008 21:00
Documentation / planning for the commands to run in a graceful failover, appear to be very straightforward and textbook. However, if the link were to be cut in a real dr, and the link goes partitioned - what are the device states at the R2 side? (RW, WD?) Thanks!
MarcT2
131 Posts
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June 26th, 2008 04:00
The R1 then "realises" it has local invalid tracks and begins to read them across the link to sync up the R1. In theory you can re-start production as soon as the links have been make RW, because host reads for tracks which have not yet been copied back will be done (at a performance penalty) across the RDF link. In practice you should consider SRDF "update"(s) prior to the failback to shift over the bulk of the data. (NB: An SRDF "update" always makes the data on the R1 inconsistient, until the failback is complete).
Once the failback is complete the SRDF state will be "Synchronised" and writes to the R1 will be synchronously mirrored to the R2 as usual.
Hope that helps!
Marc
RRR
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June 26th, 2008 04:00
I'm always confused with this... So a failback startes replicating from R2 to R1 ? So when the R1's and R2's are sync'd you need to resume the replication again to get the normal replication process going again from R1 to R2 ?
RRR
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June 26th, 2008 04:00
It's even easier than I thought !
xe2sdc
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June 26th, 2008 06:00
RRR
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vincent_corona
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June 30th, 2008 06:00