I ran into an interesting issue the other day. We were seeing high DAVG to the SAN. I first wanted to find out if the SAN was on the HCL and I found the SAN here. Next I checked the SATP and PSP settings, I saw the following:

# esxcli nmp device list -d naa.600d02310008483bOOOOOOOO7ef9583c
naa.600d02310008483bOOOOOOOO7ef9583c
Device Display Name: IFT iSCSI Disk (naa.600d02310008483bOOOOOOOO7ef9583c)
Storage Array Type: VMW_SATP_ALUA
Storage Array Type Device Config: {implicit_support=on;explicit_support=off; explicit_allow=on;alua_followover=on;{TPG_id=1,TPG_state=AO}}
Path Selection Policy: VMW_PSP_MRU
Path Selection Policy Device Config: Current Path=vmhba37:CO:T1:L6
Working Paths: vmhba37:CO:T1:L6

# esxcli corestorage device list -d na.600d02310008483bOOOOOOOO7ef9583c
naa.600d02310008483bOOOOOOOO7ef9583c
Display Name: IFT iSCSI Disk (naa.600d02310008483bOOOOOOOO7ef9583c)
Size: 1907468
Device Type: Direct-Access
Multipath Plugin: NMP
Devfs Path: /vmfs/devices/disks/naa.600d02310008483bOOOOOOOO7ef9583c
Vendor: IFT
Model: S16E-G1240
Revision: 373S
SCSI Level: 4
Is Pseudo: false
Status: on
Is RDM Capable: true
Is Local: false
Is Removable: false
Attached Filters:
VAAI Status: unknown
Other UIDs: vml.0200060000600d02310008483bOOOOOOOO7ef9583c533136452d47

The main thing that stood out was the fact that the SATP that claimed this LUN was VMW_SATP_ALUA and the Pathing Policy is VMW_PSP_MRU. If VMW_SATP_ALUA Claimed the device that means the array responded to our SCSI INQUIRY with the TPGS flag on. More information on how ALUA works can be found in article It All Started With This Question…. Checking out all the SATP rules for ALUA, I saw the following:

~ # esxcli nmp satp listrules -s VMW_SATP_ALUA
Name Device Vendor Model Driver Transport Options Claim Options Default PSP PSP Options Description
VMW_SATP_ALUA NETAPP tpgs_on VMW_PSP_RR NetApp arrays with ALUA support
VMW_SATP_ALUA IBM 2810XIV tpgs_on VMW_PSP_RR IBM 2810XIV arrays with ALUA support
VMW_SATP_ALUA tpgs_on Any array with ALUA support

So for SATP the claim option tpgs_on is the same as the TPGS flag on. The customer logged into his Infortrend account and download the Manual for the array. From the Manual we found the following:

TPGS (Target Port Group Support) concern:

Infortrend’s multi-pathing service supports TPGS and is able to designate specific data paths as Active and the non-optimal paths as Passive. With TPGS, most I/Os will be directed through the Active paths instead of the Passive paths. The passive paths only receive data flow in the event of Active path failures.

The diagram below shows a dual-controller RAID system with multi-pathing cabling:

  1. There are 4 data paths between RAID system and host. 2 from controller A and 2 from controller B.
  2. A RAID volume is managed by controller A and associated with both controller A and controller B IDs.
  3. TPGS recognizes data links from controller A as Active paths and those from controller B as Passive paths.

The Array did have two controllers so ALUA is enabled by default and there is no way to disable it. From the above HCL page the only supported SATP and PSP for that array were VMW_SATP_DEFAULT_AA and VMW_PSP_FIXED, respectively. The manual was pretty old and the array is now an A/A array instead of on an A/P array. So we decided to add a new SATP rule to match the above array and mark it as an Active/Active Array instead of an ALUA array. I found VMware KB 1026157 which had instructions on how to add a new SATP rule. First we had to determine the vendor and model of the array. That can be done by issuing an esxcfg-rescan and then looking at the logs, here is what we saw:

May 10 18:04:36 vmkernel: 429:22:55:15.800 cpu23:83814135)SCSIScan: 1062: Path 'vmhba37:C0:T1:L7': Type: 0x0, ANSI rev: 4, TPGS: 1 (implicit only)
May 10 18:04:36 vmkernel: 429:22:55:15.817 cpu23:83814135)SCSIScan: 1059: Path 'vmhba37:CO:T1:L8': Vendor: 'IFT ' Model: 'S16E-G1240 ' Rev: '373S'
May 10 18:04:36 vmkernel: 429:22:55:15.817 cpu23:83814135)SCSIScan: 1062: Path 'vmhba37:CO:T1:L8': Type: OxO, ANSI rev: 4, TPGS: 1 (implicit only)
May 10 18:04:36 vmkernel: 429:22:55:15.835 cpu23:83814135)SCSIScan: 1059: Path 'vmhba37:CO:T1:L9': Vendor: 'IFT ' Model: 'S16E-G1240 ' Rev: '373S'
May 10 18:04:36 vmkernel: 429:22:55:15.835 cpu23:83814135)SCSIScan: 1062: Path 'vmhba37:CO:T1:L9': Type: OxO, ANSI rev: 4, TPGS: 1 (implicit only)
May 10 18:04:36 vmkernel: 429:22:55:15.849 cpu23:83814135)SCSIScan: 1059: Path 'vmhba37:CO:TO:LO': Vendor: 'IFT ' Model: 'S16E-G1240 ' Rev: '3730'
May 10 18:04:36 vmkernel: 429:22:55:15.849 cpu23:83814135)SCSIScan: 1062: Path 'vmhba37:CO:TO:LO': Type: Oxd, ANSI rev: 4, TPGS: 1 (implicit only)
May 10 18:05:08 shell[83810119]: grep SCSIScan /var/log/messages

From the above output, we put together the following SATP rule for the Array:

~ # esxcli nmp satp addrule -V 'IFT' -M 'S16E-G1240' -o tpgs_on -e 'Infortrend' -s VMW_SATP_DEFAULT_AA

We then double checked that the rule has been added:

~ # esxcli nmp satp listrules -s VMW_SATP_DEFAULT_AA | grep IFT
VMW_SATP_DEFAULT_AA IFT S16E-G1240 tpgs_on Infortrend

After that we unclaimed one LUN to make sure it’s working:

~ # esxcli corestorage claiming unclaim -t location -A vmbha37 -C O -T 1 -L 6

To check that the ‘unclaim’ worked, we try to see if we can get information regarding that LUN and we fail:

~ # esxcli nmp device list -d naa.600d02310008483bOOOOOOOO7ef9583c
Errors:
Unknown device naa.600d02310008483bOOOOOOOO7ef9583c

That looks good. As a side note, if you had multiple paths for a LUN you can unclaim them and reclaim them with one big swoop by running the following:

~ # esxcli corestorage claiming reclaim -d naa.600d02310008483bOOOOOOOO7ef9583c

But I had one path so it didn’t make a difference. We then ran an esxcfg-rescan to reclaim the device and then double checked the settings to see the following:

~ # esxcfg-rescan vmhba37
~ # esxcli nmp device list -d naa.600d02310008483bOOOOOOOO7ef9583c
naa.600d02310008483bOOOOOOOO7ef9583c
Device Display Name: IFT iSCSI Disk (naa.600d02310008483bOOOOOOOO7ef9583c)
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type Device Config: SATP_VMW_SATP_DEFAULT_AA does not support device configuration.
Path Selection Policy: VMW_PSP_FIXED
Path Selection Policy Device Config: {preferred= vmhba37:CO:T1:L6;current= vmhba37:CO:T1:L6}
Working Paths: vmhba37:CO:T1:L6

We could’ve reclaimed all the LUNs by running the following:

# for i in `ls /vmfs/devices/disks/ | grep naa.600d` ; do esxcli corestorage claiming reclaim -d $i ;done

But I decided to reboot the host to make sure everything worked as expected. After the reboot we saw the following:

~ # esxcli nmp device list | grep 'Storage Array Type:'
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_LOCAL
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_LOCAL
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type: VMW_SATP_DEFAULT_AA

No SATP of VMW_SATP_ALUA was seen and the DAVG to the array lowered.


Published by Karim Elatov

25 June 2012

Tags