** Question about LUNs on a VA7400 **

[Michael Gretton]

Hi all:

I have LUNs defined on my VA7400 and one of my servers uses these for an oracle database. I would like to have another server be able to read this LUN data (not write to it!) so that I can perform backups. Is this possible or am I asking the SAN to do too much? I would assume that this capability has to be there in some respects when you go to a failover configuration.

I realize that you can configure other WWNs so they can read luns but how do you configure the other server to mount those LUNs so that it can read them?

[steven Burgess_2 · Accepted solution]

Hi

I would think the best way to do this would be to put the servers in a service guard environment. This would mean that both servers can access a volume group and it's associated physical and logical volumes.

The situation has a high potential for data corruption unless you use software to prevent data being written to the disks from both servers such as lock manager

A volume group can be marked as part of a MC/ServiceGuard cluster. When such
a group is activated in exclusive mode, it can be accessed for exclusive
read-write activity by only one of the systems at a time; the other systems
can have read-only access to the data.

Without MC/ServiceGuard, LVM does not provide protection in the case of
two systems accessing the same disk, activating the same volume group,
and writing to the same mounted file system's file simultaneously.

Have a look at the man pages for vgchange for further info on the above

HTH

Steve

[Leif Halvarsson_2]

Hi
This can be a problem. You have a FC disk with one LUN used for a filesystem mounted on one computer. If you don't use LUN zoning another computer can see this lun as an unused disk but don't know anything about filesystems, volumegroups etc.. Perhaps it is possible to import it but I don't think this is recommended.

There is a product on the market, Veritas cluster file system, that could be an alternative for you (but I think it is rather expensive).

Why do you want to back up this filesystem from another computer, I can see no advantage with this.

[Jeff Schussele]

Hi Michael,

Although you can do this, mount a VG r/w & again as r/o, I think this will be problematic for backups. The reason being is the files will be in use at the time of backup.

The way this is normally done is to have mirror copies & split one of the mirrors off & back that up. This way the files will be static.

EMC uses a similar strategy in their SW called BCV (Business Continuance Volumes).

Rgds,
Jeff

[Eugeny Brychkov]

The best solution for you is to do as the following:
a) shut down database
b) create business copy LUN
c) start database
d) do backup of business copy
e) shut down database
f) copy data from BC LUN to parent
g) start database
h) delete business copy LUN
This way you'll have min database downtime, and database will be correctly 'closed' in backup image
Visit http://www.hp.com/products1/storage/products/disk_arrays/modular/business/overview/index.html
Eugeny

[Trevor Parfitt]

I would not copy the BC back to parent as all work done on the database between steps c&g would be lost.

[Trevor Parfitt]

You will have to BC all LUNs that have any of the databases datafiles/control files on them.It should be possible to do this without shutting down the database but putting it into hot backup mode.You could then BC the database and transaction logs and restart the database on the other machine.
I have been testing this with a sybase database and use the attached script.If you are using secure manager as well as business copy you will need allow access to the BC after creating it.

[Eugeny Brychkov]

Great point! I recommend everyone before using business copy to read its manual and to have clear action plan HOW it shoul be done. Of course, if database can be switches to secure mode then you may not shut it down. For parent LUN copy I remember that BC works in the following way: when you create BC LUN then old LUN get 'frosen' and all new data writes go to BC LUN. So, primary LUN is available for backup. After backing up newly written to BC LUN data should be flushed to original LUN. That's my vision... Sorry as I may be wrong. As I said - read documentation! RTFM!
Eugeny