Informix on HPUX 11.11

[Jonathan Kamminga]

Hi Gurus,

Is it true that Informix has to write in two places? The way our Informix admins want us to present them disks from our disk array is to offer up x2 RAID0 LUNS of equal size from different RAID groups. Informix then mirrors the I/O at the host. I don't understand this, and I have tried to explain why this is dangerous, but they insist that this is correct. It appears to me to be an old way of thinking - from the days of SCSI attached JBODS??

Any insight to this is greatly appreciated!

JK.

[Steve Lewis]

Your informix DBAs want to set up informix mirroring of striped logical volumes.

If you storage is just striped lvols and not mirrored, then it is safer to use some kind of mirroring or RAID parity as well. It could be made to work well.

If your storage is already mirrored, or is a RAID 0/1 LUN, then it will be much better to not use informix mirroring on top, because it is unnecessary and slower.

[Jonathan Kamminga]

Thanks Steve,

This is what I thought, but they tell me that they "have" to mirror at the Informix level - the application requires it! I would have thought that they could turn off Informix mirroring - couldn't they??

Rgds,

JK.

[Steve Lewis · Accepted solution]

You are quite correct. You do NOT have to mirror at the informix level. I even recommend that you don't mirror at the informix level. It is inefficient and its a right pain when a disk breaks. Much better to mirror in the disk array.

When you create an informix dbspace, you tell it the chunk path using a command like:
onspaces -c dbspacename -p path -o offset -s size

The onspaces command (which you can get the synopsis by typing onspaces -- ) shows the mirror path in []s which proves they are optional.

Then you just add more chunks to the dbspace using onspaces -a dbspacename -p path -o offset -s size

[Jonathan Kamminga]

Excellent! Thanks Steve.