Raw volumes vs VxVM raw volumes for Oracle ASM?

[RaviSS]

Hi,

A customer wants to understand if there is any performance impact if using VxVM raw volumes instead of just plain old raw volumes for creating ASM diskgroups.

We recommended VxVM due to flexibility and ease of management. Any real world numbers or a document we can refer him to to ease his concern?

Thanks,
Ravi

[TTr]

> instead of just plain old raw volumes

What are these "plain old raw volumes"? The disk devices themselves or LVM volumes?

And what does VxVM give you that LVM does not? (other than a very expensive bill)

What OS version?

[RaviSS]

Sorry. I meant raw devices. OS is 11.31

[chris huys_4]

Hi,


> A customer wants to understand if there is
> any performance impact if using VxVM raw
> volumes instead of just plain old raw
> volumes for creating ASM diskgroups.
Pff, Im not a big fan from asm, substandard product, and gives oracle dba's to much leverage over system admins qua maintenance of the system. ;)

> We recommended VxVM due to flexibility and
> ease of management. Any real world numbers
> or a document we can refer him to to ease
> his concern?
I would go for plain raw disk devices. You know the oracle dba's will begin almost instantly about performance problems, due to asm, and its better to not have vxvm in the mix, to avoid them pointing to vxvm as being the culprit. (also asm is and a volumemanager and a cluster solution and a database manager, so replacing one of this components by another product, is asking for euhm, confusion, let them have it all or nothing.. ;) )

> And what does VxVM give you that LVM does
> not? (other than a very expensive bill)
Less prejudices. ;) (sorry couldnt let that slide) For the rest if lvm, would be able to have a shared filesystem, like vxvm with cfs has, I would understand your point, but as it doesnt..

Greetz,
Chris

[Raj D. · Accepted solution]

RaviSS,

I have seen ASM with oracle 10g it works well with LVM and VXVM mixed mode . create a vxvm dg with simple disk type and the raw devs, remember /dev/vx/rdsk//rawvolXX path for linking:

Ex:
ora_ASM_dg

crw-rw---- 1 oracle dba 58 0x000012 May 3 10:42 ora_ASM_flashbackx1
crw-rw---- 1 oracle dba 58 0x000013 May 3 10:42 ora_ASM_flashbackx2




crw-rw---- 1 oracle dba 58 0x06216b Jun 3 11:04 ora_ASM_028
crw-rw---- 1 oracle dba 58 0x062176 Jun 3 11:31 ora_ASM_029


There is another discussion :
http://forums13.itrc.hp.com/service/forums/questionanswer.do?&threadId=1238450



- Also check out the symantec document:
Nicely explained how to create ASM diskgroup with vxvm devices:

http://eval.symantec.com/mktginfo/enterprise/white_papers/b-whitepaper_integrating_oracle_automatic_01-2008.en-us.pdf


Cheers,
Raj.

[TwoProc]

I'd use lvm. No doubt about it. I *do* have a small amount of CPU consumed at peak with vxfsd, but this is scatted amongst about a hundred threads which at any point in time almost always seem to be waiting on SLEEP ( I checked and watched my system for a while today).

And - that vxfsd process is, from what I've read - cpu resources for using FILE SYSTEMS in lvm, not for lvm itself. Therefore, if you've got no file systems in the lvm volumes themselves, you would probably have none of this cpu type activity.

Can anyone else confirm that vxfsd process if for *file systems* using lvm, and would not be used for lvm volumes that are raw?

According to the man page, it says that vxfsd is processing for file systems using lvm. However, the man page may have meant logical volumes, not file systems.