Splitting mirrors on AIX 4.3 1

[Guest_imported]

Hi everybody,

We have the "problem" that our (Oracle) backups take up a
long time. In case of an offline backup far TOO long.
Al our lv's are mirrored (2 copies). Is there a
possbility to bring the database down, split the mirrors,
bring Oracle up again, backup the detached disks and
resync them afterwards ?

I would appreciate any information on this topic ?

Thanx 'n' Rgds.

 

[PSD]

Bobo,

Well there are two avenues you could look at:

1) The splitlvcopy command - this copies the lv to a new lv thus splitting the mirror.....I have used this before with success.

2) rmlvcopy, mklvcopy and synvg i.e. to remove, recreate ans re-sync to the copy....you can script this in....

Hope this helps?

Cheers

PSD
HACMP Specialist

p.s. Have you looked at RAID 10 - striping and mirroring through the 4-P SSA adapters?? This would improve I/O performance by 40-60% in my experience.

 

[aixqueen]

ONLINE JFS BACKUP (Split Mirroring) In AIX 4.3.3
This is triple split mirroring backup. It takes a system that is 3 way mirrored,
makes a split off of one of the mirrors, and then backs it up, then reintegrates
a mirrored copy. It is creating a snapshot of the logical volume that contains
the file system. Logical volume and its JFS log logical volume MUST be
mirrored. File system activity should be minimal (quiescing) while the split is
taking place.
It is my understanding that this can be done with only two copies, but the
user is less protected in case of disk failure. Making an online backup of a
mounted JFS file system has several rules. One is that the data that was
written immediately before the snapshot is taken will not contain those
changes. Modifications that start after the snapshot begins may not be
present in the backup copy as well.
You will use the splitcopy command to make this happen.

#chfs -a splitcopy=/backup -a copy=3 /testfs

to reintegrate a mirrored copy simply remove the backup file system by using
the rmfs command
# unmount /backup
# rmfs /backup

http://www.rs6000.ibm.com/doc_link/en_US/a_doc_lib/cmds/aixcmds1/chfs.htm

=========================
As stated you can do the splitlvcopy command as well.
To split one copy of each logical partition belonging to logical volume named oldlv
which currenttly has 3 copies of each logical partition, and create the logical volume
newlv, enter:

splitlvcopy -y newlv oldlv 2

Each logical partition in the logical volume oldlv now has two physical partitions. Each
logical partition in the logical volume newlv now has one physical partition

http://www.rs6000.ibm.com/doc_link/en_US/a_doc_lib/cmds/aixcmds5/splitlvcopy.htm

.
The newer levels of Sysback, it is my understanding also breaks the mirror, backs it up and puts it back....Sysback is a separate product that IBM sells.

One last word of caution. the redo logs....Are you bringing the system down and stopping the logs before backing them up? If not, a restore could be interesting since the timestamps may be off. Some have done an export of the tables to a filesystem and backed that up during the night....others use sysback, but the problem is the same if the data is not stagnant.

Good Luck
#-)

 

[Guest_imported]

Thanks all for the great info !!!

To answer aixqueen's last question.

As we have a nightly time frame to do offline backups,
we might as well pull Oracle down, split the mirror and
mount the lv's on new filesystems and then restart
Oracle. We 'should' then be able to take a full consistent
backup of the FS copies without having to recover the
redologs if/when lightening strikes ...
During the week have our regular online backup scheme
without archived log backups.

Anyway, knowing all this, I think we'll manage. Thanks
again. You have my vote

 

[aixqueen]

Well Please be careful...and test.. there is... .nothing worse then trying to restore a database and having it fail.........I would definitely do a trial and error on splitting and
seeing if you can restore somewhere else and bring it up.......

You might also want to check Oracle out and see what they recommend on the rs6000

There are a lot of redbooks on database and backup strategies

http://www.redbooks.ibm.com/

Using ADSM to Back Up Databases,
SG24-4335-03

AIX Logical Volume Manager, From A to Z:
Introduction and Concepts, SG24-5432-00

Database Performance on AIX in DB2 UDB and
Oracle Environments, SG24-5511-00

Might be worth a look...