2 luns in one raw disk for oracle RAC

[Angel Dino Hornos]

Hi Everybody

I have to create a /prod/rdsk/disk01 (raw) for an oracle 11g over hp-ux 11.31 with two LUNs from external storage (/dev/rdisk/disk145 & /dev/rdisk/disk145) both luns are 1TB size and the /prod/rdsk/disk01 has to be 2TB, i mean lun1+lun2, i've really didnt find anything regarding this, could you please help me
thank you very very much for your time

[TTr]

> with two LUNs from external storage (/dev/rdisk/disk145 & /dev/rdisk/disk145) both luns are 1TB size

Unless oracle can combine the two LUNs into one from their native paths, you have to use LVM and combine the two LUNs into one logical volume. The problem is that you can't use the /prod/rdsk/disk01 path, you have to use a standard VG/LV path. (Actually you could but you would have to dedicate the /prod/rdsk path as the volume group path and disk01 as the LV path).

Why can't you use the two LUNs directly in oracle? You will get double the i/o that way (two i/o devices as opposed to one with LV).

[Angel Dino Hornos]

Hi TTr sorry about the typo when i wrote /dev/rdisk/disk145 & /dev/rdisk/disk145 ( this last one is /dev/rdisk/disk146) those are two different luns presented to the same server, and i should do just one raw disk.

yes oracle can use both disks, but i should define first /prod/rdsk/disk01 with those two luns, it should be raw because they are going to use ASM only, but i don't have a clue for how to do this without slvm.

Thank you very much for your time

[Torsten.]

For such purposes volume managers (LVM) are made.

[Shibin_2]

Are you System Admin ? If not, ask you SA to do for you.

You can either user LVM or VxVM to do this job.

[Rita C Workman]

What kind of disk array do you have?

For example, on an EMC Symmetrix, the storage person could take those two disks and combine them into one meta-disk.
Then re-present them to the server as ...tada... "one disk".

Sometimes disk solutions can be easily handled from the storage perspective and not the server perspective.

Rgrds,
Rita

[Angel Dino Hornos]

Shibin, yes i'm the SA of that server, and yes Torsten you're right LVM could be a good choice, but they need raw device for asm because inode contention in other servers with lvm due to the I/O rate needed, ASM uses raw devices in this case, and dba team fixed with that in other server, but with 1 lun 1 disk.
do you think that there is a way to do this (2 luns 1 raw disk) without going througt storage team with a meta-device?

Guys really thank you very much for your time and answers

[Torsten. · Accepted solution]

Of course you can use a LVM LVOL as a raw device ...

[Shibin_2]

Hi Angel, it is interesting.

We had a similar setup in one of our environment. What we did was, create LV and link the raw device of LV to the directory what they really need.

That's you, do pvcreate, vgcreate, lvcreate etc. ( I guess, we does mkfs too, can't remember. Few years back we did ). Then link the /dev/vg/rlvol to the directory.

Ultimately it will looks like this.

/dev/vg/rlvol --> /prod/rdsk/disk01

I hope this will help.

[TwoProc]

Take your two disk devices, and use lvm to make then into volume group. Then, take ALL of the extents from the volume group and cut out of there a single lvol. Now, to use it as raw, just don't format it. Now you've got a single disk that represents both raw volumes as one, and you're done.

For performance reasons, I'd use extent based stripes across the two real devices to create your lvm based logical volume.

Keep in mind that lvm (logical volume manager) just manages /dev/ disks to create logical volumes --->>> not "file systems".

Just because folks commonly put file systems on logical volumes, does not mean that you have to. You can use lvm allocated lvols (ne' raw disks of a virtual sort) in raw mode as easily as you can actual raw volumes from your EMC storage system.