luns

[A.G.M. Velthof]

Hello to all,

we are planning a new Oracle cluster with storage on 2 Eva's, using hpux 11.31.
Per Oracle instance we need 80 GB storage.
Is there still any reason for us to create
4 x 20 GB from performance point of view or is it sufficient to create 1 x 80 GB.

[Sachin Kumbla]

Hi

If you are using 4 luns to create a 80gb FS then the only advantage will be i/o on disks will be reduced if you use stripping while creating the LVM.

This will give a better performance.

Rgds.,
Sachin Kumbla

[Johnson Punniyalingam]

As post above by >>Sachin Kumbla <<

Oracle recommends the same "Logical volume to stripped while creating" for better performance,

[Johnson Punniyalingam]

Benefits of striping:

1) Increase the performance of applications that read and write large sequentially accessed files. Striping with randomly accessed files yields inconsistent performance.

2) If each of the disk has their own controller instead of using a common
controller, each can process and transmit data simultaneously, resulting in further performance gains.

3) You can use familiar, standard comands to manage your striped disks, i.e. lvcreate, diskinfo, newfs, fsck, mount, all work with striped disk.

Drawbacks of Striping:

1) Since disk striping uses multiple disks, there is a greater likelihood of disk failure for any one of them, thus requiring restoring from backup (if not mirrored).

2) More complexity occurs when some of the disks have both striped and non-striped logical volumes. It is recommended, but not required that all the logical volumes within the same volume group be striped.

3) Since it is recommended that all the logical volumes within the same volume group be striped, if one of the disks goes bad, then recovery of multiple filesystems may be needed.

4) Performance could actually decrease if your disks are on the same controller and the I/O for one disk has to wait for completion of I/O on another disk.


Other considerations:
----------------------
1) Best performance occurs from a striped logical volume that spans similar disks. The more closely you match the disks in terms of speed, capacity, and interface type, the better the performance. For example, when striping across several disks of varying speeds, performance will be no faster than the slowest disk.

2) If you have more than one interface card or bus to which you can connect the disks, distribute the disks as evenly as possible among them to achieve best I/O performance.

[A.G.M. Velthof]

Even if it is on a EVA? Is the performance advantage worth it to create 4 instead of 1?

[Sachin Kumbla]

Hi

Yes Velthof I can very well understand your issue that an from EVA a chunk is presented instead of LUN.

It depends upon the usage & criticality of your organisation.

Rgds.,
Sachin Kumbla

[A.G.M. Velthof]

Ok, thank You both for the answers.

Greetings, Alfons