how many volume groups for oracle?

[Doug Wilburn]

I'm new to HPUX/LVM coming from Tru64. I have an rx2660 running HPUX 11i3 and an EVA6400. My oracle dba wants 4 directories for data. Should I create one vg with 4 lv's? or one vg for each lv? And, when I create the lv's and mount them, do I have to manually add it to /etc/fstab - I had to in Tru64?

[John Dvorchak]

I would create 4 new VG's each with one LV for performance and future expansion if you have the free disks/luns to do so.

As for adding the mount points in /etc/fstab yes. Get the mount options from your DBA as well as getting the suggested layout for the file systems like sripe width and block size.

[Mel Burslan]

At this point, your only concern regarding the number of VGs is if you can handle all the LUNs presented to this system under a single volume group ? Which yields to what size of LUNs you are presenting and what are you going to use Max PE per VG value ? Spreading of LUNs over several volume groups, do not have much to do with the disk performance. Disk performance in my opinion is more related to how the physical spindles are spread inside the EVA array for the LUNs you create. But VGs are a good way to segregate functions of volumes. For instance, Oracle runs best (this is my latest dba's word, not mine) with PE size of 8 MB per physical extent on the database container volumes, whereas log files (origlog and mirrlog volumes), can do with 1M extents. And extent size can be specified at the VG level.

If you have an oracle support agreement, it might be a good call to their support and see what is best for your circumstances as far as data and log extent sizes.

[Steven E. Protter]

Shalom,

Issues:

* Getting maximum number of disk heads for fast data access. Generally taken care of on the SAN side, but still, striping is used to assist.

* LUN size. Generally expansion should be handled through adding a new LUN and then extending the logical volume.

* Access type. Oracle writes archive logs sequentially and will do well with raid 5 parity 9 storage. Heavy read/write environments need different configuration.

* This assumes there is no ServiceGuard High availability clustering.


* How many total disks/luns available on the EVA6400.

I don't think your DBA is off base. This plan offers a lot of flexibility.

SEP

[Doug Wilburn]

Thank you all for quick responses. I have a couple more questions. Can I create 1 lv in each vg to be the same size of the vg? Are there advantages/disadvantages of doing it this way?

[Steven E. Protter]

Shalom,

Answer to second question.

You can do with 4 volume groups and 4 lv's covering each volume group.

Advantages: You can configure each one custom, with striping if you wish for maximum performance.

Disadvantage: Many people like to have a single database instance in a single volume group. This makes activation simple, and going with high availability like ServiceGuard less complex.

You can customize the lv's as you build them in a single volume group.

I like having a volume group contain a single database instance, making it ServiceGuard ready in the future. It will still work with 4 volume groups, but in my opinion adds needless complexity.

SEP

[Doug Wilburn]

Thanks to all for the good information and advice.

[Alzhy]

Doug,

Since you have an EVA, it does not matter if you do one VG with multiple LVs (you can always spec out which PV you carve for which LV) and vice versa.

What is IMPORTANT is you carve 4 Vdisks out of your EVA8400 and alternate path preferencing of the Vdisks between the 2 Controllers for optimal performance.

Now -- since it seems your DBA prefers cooked or filesystem based Oracle data storage... please bear in mind the recommended "MOUNT" options for filesystem based Oracle storage. And depending on your version of VxFS installed -- If VxFS 4.0/t.0:

delaylog,convosync=direct,mincache=direct

If VxFS (aka OnlineJFS) is 5.0.1:

cio,delaylog

Using the cio mount option implies the use of mincache=direct and conosync=direct.

You may also wish to Google a document tieled "HP-UX VxFS mount options for Oracle Database environments" as there are helpful tunables for both the OS admin and DBAs alike.