When creating a logical volume, one of the requirements is to choose
the number of logical partitions.

Is there any way to determine an optimal number of partitions to
enhance performance?

Currently, I am creating a logical volume, using EMC disks, the luns
are 8.5GB, the volume group is roughly 50GB.

I am not real familiar with AIX, so any information/explanations would
be appreciated.

Thanks,
Jeff

Hi Jeff,

Partitions are created at the volume group level, and you will have a
certain number of partitions based on the setting for PP size for that
VG. For a 50 GB volume group, you can have a PP size no smaller than 64
MB. This is based on the following calculation:

MAX_PPs * PP_SIZE = MAX_MB

eg. 1016 * 64 = 65024 (or roughly 64 GB)

Based on the calculation, you could potentially expand your 50 GB
volume group up to 64 GB before you ran into an issue where you had
reached the maximum number of physical partitions that can be assigned
to a volume group.

At the logical volume level, you select your partitions based on what
part of the disk you want to use. For example, most often used data you
may want to be in the fastest accessed part of the disk (middle), or
you may want to put it on the outer edge since that contains the
largest number of partitions.

I don't believe that there is a magic formula for deciding what is the
optimal number of partitions for the LV, since the PP size and the
location on the disk seem to have to be factors in this calculation.
However, I guess if you use up so many PPs that you exceed the amount
in the selected section on the disk (eg. all of the middle, and some of
the inner edge) then this will affect disk access perfromance.

The IBM Redbooks are really a pretty good place to check for info on
disk partitioning. You may want to check this one out called "AIX
Storage Management":

http://publib-b.boulder.ibm.com/abst...4484.html?Open

Steve

jeff.bromley@haworth.com wrote:
> When creating a logical volume, one of the requirements is to choose
> the number of logical partitions.

This is really just a storage question. The logical size ==
the physical size which you can get via "lsvg VGNAME"

>
> Is there any way to determine an optimal number of partitions to
> enhance performance?

Performance is going to be determined mostly by how the EMC disks are
connected and configured and what sort of mix you have for read/writes
and how well the cache on the EMC is used... seens like.

Jeff,

There is no optimal setting for performance on number of partitions.
The number of partitions determine the size of the LV.
Also, the partition size is set when you created the VG.
So, if your physical partition size is set to 128MB then you divide
128 into the size in MB you desire your LV to be.
Example: LV=20GB You should have 1024*20 / 128 = 160 partitions

You can however, stripe the partitions across multiple drives for
better performance when you are creating the LV by specifying
which drives you want to stripe the LV across and setting the appropriate
stripe size.  You should base the stripe size on the application or DB
that will be using this filesystem.  This causes less I/O wait on any one
drive in the system.


Hope this helps.

--flossy




jeff.bromley@haworth.com wrote:

When creating a logical volume, one of the requirements is to choose the number of logical partitions. Is there any way to determine an optimal number of partitions to enhance performance? Currently, I am creating a logical volume, using EMC disks, the luns are 8.5GB, the volume group is roughly 50GB. I am not real familiar with AIX, so any information/explanations would be appreciated. Thanks, Jeff