secure path and pv links confusion

[shashi kanth]

I can understand secure path will enhances the PV Links functionality, but i am not getting the point with HP LVM, whether we need create the PVs with legacy device name and add all the alternate paths of that device to the PV, or create a PV with Virtual Device name assigned by secure path ?

pvcreate /dev/dsk/c4t0d1 ?

or

pvcreate /hpap/dsk/hpap0 ?

Which one is a better approach from the applications (oracle db2) point of view ?

[Ganesan R]

Hi Shashi,

I heard that in 11i v3(where legacy device is supported) supports load balancing through alternete links by default. We don't need to configure what we use to do it 11i v1 and V2.

Basically, Alternate PV links are meant to high availablity. If primary link fails, will switch over to alternate links if we have configured. We can achieve some kind of load balancing by routing some disk's to primary links and some disk's to alternate links by changing the order in vg configuration.

Secure path is dedicated load balancing software which will route the I/O's through all the routes to achieve high performance.

Hope this helps.

[Duncan Edmonstone]

Ganesan, this can't be 11iv3 as hge wouldn't even be able to install Secure Path on that...

Looking at what you've posted I'm assuming this is Secure Path for Active/Active disk arrays.

For LVM you need to use the devices in /dev/dsk - LVM won't like using the virtual devices. Choose either path to the disk, it won't matter as Secure Path will intercept the IO and use whichever load balancing algorithm you've chosen to send IO down the relevant path.

So you can choose just to put one path's device files in the volume group, or put both in. Generally I put both in as it reminds me that thoose PVs are in that G, but you don't have to.

HTH

Duncan

[Torsten.]

See this document

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00248499/c00248499.pdf

and locate

Figure 2 Driver model structure

for basic understanding.

[Sani]

Hi ,

If your are creating a VG , you have to use both primary and alternate paths.Because if one path fails , lvm will use the other path.

Secure path will do load balancing between these paths as per the configured load balancong policy.

For v3 systems secure path is not reqd.

Regards
Sani

[sujit kumar singh · Accepted solution]

Hi


Securepath provides with both the Alternate Linking as well as the Load Balancing.

So this depends if you are using RAW Space for the Disks to be used with Oracle,
you can create a VG using the Disk files and create the LVs and use that for the RAW data Storage, The same if you are using the The LVs on such VG for keeping data on the Filesystems.
Well using the Device Files /hpap/dsk/hpap0 instead of the legacy /dev/dsk/cXtYdZ will help you identify the disks properly (new device files to use that only i think so) and you can create VG also using those dev files that is /hpap/dsk/hpap0, but think what shall happen if sometimes you plan to remove the HPSP product, You will need to reimport the VGs snd you shall always have to preseve the MAP files of the VG which will be having a VGID of that VG.

Also whenever you import the VG using these map files that shall have the Device Files of the /dev/dsk/cXtYdZ style you shall have to again add the paths /hpap/dsk/hpap0 to the VG.

so a good approcah shall be like
1)keep using the legacy DSF /dev/dsk/cXtYdZ format for the Paths in the VG for a Disk.(whether you use LVs with the Filesystenms or As rar LVs for Data storage).
2)If you are not using the VGs but the whole disk Dev files for the Raw Data Storage for the Database, then better you can use the /hpap/dsk/hpap0 etc.
3)In both the case do not forget to define a load-balancing policy for the Disk that you might be using, using the invocation of the command #autopath set lb_policy
or #spmgr commands
regards
sujit

[shashi kanth]

Thank you all.