Originally posted by: SystemAdmin

Hi IBM AIX admin,

Recently, we have AIX server 5.3 installed with EMC storage for Oracle database. I am currently trying to understand disks configuration and would be easier to do troubleshooting in the future. Hope, someone would like to explain for my understanding. Thanks.

1. I did the root>powermt display dev=all and take two of the EMC virtual LUN as below

Pseudo name=hdiskpower25
CLARiiON ID=CK200074100492 myaix
Logical device ID=6006016032601E0064D8C5E8B2FCDD11 LUN 182
state=alive; policy=CLAROpt; priority=0; queued-IOs=0
Owner: default=SP B, current=SP B Array failover mode: 1
==============================================================================

---

Host

---

- Stor - -- I/O Path - -- Stats ---

1. HW Path I/O Paths Interf. Mode State Q-IOs Errors

==============================================================================
0 fscsi1 hdisk118 SP A4 active alive 0 1
0 fscsi1 hdisk98 SP B5 active alive 0 1
1 fscsi3 hdisk138 SP A5 active alive 0 0
1 fscsi3 hdisk158 SP B4 active alive 0 0

Pseudo name=hdiskpower26
CLARiiON ID=CK200074100492 myaix
Logical device ID=6006016032601E0086105CF1B2FCDD11 LUN 282
state=alive; policy=CLAROpt; priority=0; queued-IOs=0
Owner: default=SP B, current=SP B Array failover mode: 1
==============================================================================

---

Host

---

- Stor - -- I/O Path - -- Stats ---

1. HW Path I/O Paths Interf. Mode State Q-IOs Errors

==============================================================================
0 fscsi1 hdisk119 SP A4 active alive 0 1
0 fscsi1 hdisk99 SP B5 active alive 0 1
1 fscsi3 hdisk139 SP A5 active alive 0 0
1 fscsi3 hdisk159 SP B4 active alive 0 0

2. I have one Logical Vol Group created with both EMC LUN as above.

Check what EMC LUNs allocated in p7vg group
root@myaix:../oraclem:> lsvg -p p7vg
p7vg:
PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTION
hdiskpower25 active 599 298 58..00..00..120..120
hdiskpower26 active 599 299 59..00..00..120..120

3. There has 3 Logical volumes created within the p7vg group

p7vg:
LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINT
p7_lv01 jfs2 200 200 2 open/syncd /u107/ora_log
p7_lv02 jfs2 400 400 2 open/syncd /u107/ora_arch
loglv07 jfs2log 1 1 1 open/syncd N/A

4. Got to know the logical volumes using the dedicated EMC LUN
oraclem@myaix:../oraclem:> lslv -l p7_lv01
p7_lv01:/u107/ora_log
PV COPIES IN BAND DISTRIBUTION
hdiskpower25 100:000:000 100% 000:100:000:000:000
hdiskpower26 100:000:000 100% 000:100:000:000:000

oraclem@myaix:../oraclem:> lslv -l p7_lv02
p7_lv02:/u107/ora_arch
PV COPIES IN BAND DISTRIBUTION
hdiskpower25 200:000:000 10% 061:020:119:000:000
hdiskpower26 200:000:000 10% 061:020:119:000:000

oraclem@myaix:../oraclem:> lslv -l loglv07
loglv07:N/A
PV COPIES IN BAND DISTRIBUTION
hdiskpower25 001:000:000 0% 001:000:000:000:000

Can someone pls confirm my understanding?
1. At the point 1) above, each of hdiskpower25 and hdiskpower26 has 4 hdiskXX path to the EMC storage. Is it correct? or can you please explain to me clearly with the output there? Thanks

2. With the LV group p7vg, it has two EMC hdiskpowerXX LUN and they are load balanced for the LV volumes. correct?

Best Regards,
vbeer008
#AIX-Forum

Originally posted by: SystemAdmin

Yes, the powerpath software is the EMC multipathing software that you can use to get multiple paths from your HBA's to the LUN's over the SAN.

hdiskpowerXX is just a pseudo device that has one hdiskXX for each path over the SAN, you have 4 paths for each hdiskpower there... you must use the hdiskpower dev's and not the hdisk's in order to get the benefits of powerpath.....

the powerpath software does load balance the traffic, I believe this is answering your second question.. you can use iostat -a to view the traffic flowing across your fcs devics, note however that they may appear lopsided.. this has to do with how powerpath assigns the backing hdisk to the hdiskpower... you can find more info on that if you look through the PowerPath on AIX doc.
#AIX-Forum

Originally posted by: shargus

You are using EMC's Clariion array. They do load-balancing differently.

You have two service processors ("SP") - an A and a B. Even though a Clariion LUN is assigned to both SP A and SP B, only one SP can actively serve the LUN. The other SP is passive for that LUN.

Looking at hdiskpower25, PowerPath reports the following:
- It is Clariion LUN 182
- It's state is alive
- The default SP is B.
- It is currently running through SP B.
- You have four paths - two through SP A and two through SP B.
- PowerPath is smart enough to take all this into account and do the proper load balancing that is optimal for Clariions ("policy=CLAROpt").

You have two HBAs. Each connect to the two SPs (probably through a switch) such that:
1. PowerPath can load-balance the HBAs.
2. A fault in any one component (HBA, fiber, or SP) will not lose access to the disks. You would either switch to the alternate SP or lose some bandwidth.

By design, though, you cannot load-balance SPs. Only one can actively serve a given lun at a time.
#AIX-Forum

Originally posted by: SystemAdmin

Hi Fook and Shargus,

Thanks for the details explaination. It is very clear.
Just one more question on the LV group, as u see the output. hdiskpower25 and 26 are allocated for the volume group. And there has 3 logical vol sharing the both LUN. Is the PP shared by both LUN (in a concept of strip to two lun equally)? Thanks
#AIX-Forum

Originally posted by: shargus

If I understand the question correctly, no, a single LVM PP is not shared by both Clariion LUNs.

You can do lsvg <vgname> to get info on the volume group. The value for "TOTAL PPs:" is the total number of PPs available in the volume group - this should be the sum of the size of the two Clariion LUNs.

For each LVM logical volume, you can do lslv <lvolname>.
- Look for "COPIES:". This number will tell you how many mirror copies there are. Possible values are 1, 2, or 3. If the logical volume is mirrored, then each logical partition ("LP") occupies two (or three) physical partitions ("PP").
- Look for "STRIPE WIDTH:". This will tell you if your logical volume is striped at the LVM layer.

To get a detailed list of which disk has which LP, use lslv -m <lvolname>. This list may be quite long.
- A mirrored logical volume will have multiple columns as each LP has multiple PP copies.
- A striped logical volume will show consecutive LP's mapped to PP's on alternate disks.
#AIX-Forum