IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 7. Open systems servers - UNIX 239

OPEN LVs: 0 QUORUM: 5

TOTAL PVs: 8 VG DESCRIPTORS: 8

STALE PVs: 0 STALE PPs: 0

ACTIVE PVs: 8 AUTO ON: yes

MAX PPs per PV: 5080 MAX PVs: 25

LTG size: 128 kilobyte(s) AUTO SYNC: no

HOT SPARE: no BB POLICY: relocatable

The new volume group has a good physical partition size; room for 3 more sets of LUNs, so

plenty of room for growth here. What more could you want out of a volume group? Except that

the LTG size did not change to 256 KB. We could not get this to work from the command line.

However, the following command will fix this:

chvg -L 256 6000vg

With AIX 5.3, the LTG size is automatically set, so the chvg or mkvg commands do not apply.

7.8.2 Creating a logical volume

After creating the volume group, next you create the logical volumes in the volume group.

Here a choice exists for using non-striped logical volumes or striped logical volumes. Striped

logical volumes come in two styles, striped or maximum inter-policy striped.

For randomly accessed logical volumes, we recommend using the maximum inter-policy,

which also is referred to as the inter-disk policy. To make striped logical volumes using the

inter-disk policy, use the -e x flags on the mklv command.

The DS6000 is capable of exceptional throughput for the different types of I/O. Understanding

your I/O workload characteristics (see Chapter 12, “Understanding your workload” on

page 407) will allow you to further maximize the performance gains you obtain from the

DS6000. In order to choose the best type of logical volumes to create, It will be necessary to

know which of the following is more predominant in each of your applications:

򐂰 Lots of small random I/O operations

򐂰 Large sequential I/O operations

򐂰 A combination of the above

Below is an overview of the three types of logical volumes.

Non striped logical volumes

Figure 7-5 on page 240 shows a 128 MB logical volume on a single LUN. In this figure we use

vpath0, which is an 8 GB LUN on the DS6000. As we already know, the LUN is

hardware

striped

by the DS6000 in a RAID 5 or RAID 10 array. If the Rank is RAID 5 (7+P), for example,

then vpath0 will be striped across 8 DDMs.

Note: We recommend the maximum inter-policy logical volume for randomly accessed

data. This logical volume is created using the -e x flag of the mklv command. Or in smit,

set the RANGE of physical volumes to maximum and specify all the vpaths in the volume

group.