Physical volume groups and Sympath

[System_2]

Hello,

Is it usefull for performance or anything else to use LV with Allocation=PVG-strict/distributed when we are using EMC/sympath disk?

Also do the Alternate links need to be added to the /etc/lvmpvg file?

Thanks.

[Devender Khatana · Accepted solution]

Hi,

This is used for extent based mirroring i.e. when you want two copies of you data on two different set of disks. If you are not mirroring at LVOL level then there will be no benefit out of it. Rather use stripping across multiple LUNS for better performance.

Also alternate links needs to be added to /etc/lvmpvg file.

HTH,
Devender

[Devesh Pant_1]

It will be detrimental to your performance

Yes, you will have to add the alternate links to the lvmpvg file.

Devesh

[Madhusudhan_3]

Hi

It depends on the purpose of the file system you are using.

In our case, we use PVG-strict policy for all lvols in one of the VG(used for Oracle databse). By doing this we avoid, data files, archive logs, redo logs going to the same physical disk.

I don't think, you get any performance difference by doing this as you are using storage array. Only the allocation of different types of files to different disks acheived.

regards,
Madhu

[System_2]

Thank you all for the quick and helpfull reply. Just a few more questions.

Devender,
Do you mean LVM stripping or Symmetix level stripping? Currently we are using RAID 0+1 at the Symm level.
Also does the listing order of the c#t#d# within a PVG matter?

Devesh,
How bad would it be? which way would you recommend for an Oracle data warehouse?

Madhu,
We have 59 PVG-strict/distributed logical volumes of 67GB each. Those 59 LV on 10 VGs. Those VGs are made of 6 (67GB) EMC LUNs which in term made of a RAID 0+1 physical disks. Our Oracle files are distributed across and mix in the 59 LVs. Any recommendation?

[Devender Khatana]

Hi,

From this I meant LVM level mirroring only. These LVs across which your files are distributed could have been stripped across 6 LUNs of each VG. This will make more sense if your LUNs are created using less no. of physical disks. Also while creating a VG of these LUNs prior to putting entry in /etc/lvmpvg file divide 6 LUNs of each VG in a two groups of three each. Now create VG having taken one controller of first three and second controller for second three. Now add second controller for first three and first controller for second three as alternate link. This shall give you a stripping at controller level also. This also improves performance as both controllers are utilized simultaneously. Otherwise LVM supports multiple paths in active-standby mode and not active-active mode.

HTH,
Devender

[Devender Khatana]

Hi,

Also have a look at this thread.

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=868994


HTH,
Devender