Administrator Guide

VMware vSphere and Live Volume
50 Dell EMC SC Series: Synchronous Replication and Live Volume | CML1064
Note: ALUA information used by the Round Robin PSP for a device can also be viewed using esxcli as
shown in the following example. TPG_state identifies the active/optimal and active/non-optimal ALUA state
for each target port group. Working Paths identifies each active/optimal path for Round Robin as derived
from the target port groups.
[root@s1212:~] esxcli storage nmp device list -d
naa.6000d31000ed1f000000000000000015
naa.6000d31000ed1f000000000000000015
Device Display Name: COMPELNT Fibre Channel Disk
(naa.6000d31000ed1f000000000000000015)
Storage Array Type: VMW_SATP_ALUA
Storage Array Type Device Config: {implicit_support=on; explicit_support=off;
explicit_allow=on; alua_followover=on; action_OnRetryErrors=off;
{TPG_id=61480,TPG_state=ANO}{TPG_id=61731,TPG_state=AO}{TPG_id=61735,TPG_state=A
O}{TPG_id=61732,TPG_state=AO}{TPG_id=61475,TPG_state=ANO}{TPG_id=61736,TPG_state
=AO}{TPG_id=61479,TPG_state=ANO}{TPG_id=61476,TPG_state=ANO}}
Path Selection Policy: VMW_PSP_RR
Path Selection Policy Device Config:
{policy=rr,iops=1000,bytes=10485760,useANO=0; lastPathIndex=6:
NumIOsPending=0,numBytesPending=0}
Path Selection Policy Device Custom Config:
Working Paths: vmhba3:C0:T15:L1, vmhba2:C0:T15:L1, vmhba3:C0:T14:L1,
vmhba2:C0:T14:L1
Is USB: false
If a Live Volume role swap occurs, the SC Series array is designed to report the ALUA path state changes to
the vSphere host using the following process (according to the T10 SCSI-3 specification SPC-3):
1. A Live Volume role swap occurs between optimal and non-optimal paths.
2. The vSphere hosts send Round Robin I/O to what is now the secondary Live Volume through non-
optimal paths.
3. The SC Series array fails the I/O with a Unit Attention Check Condition.
4. The vSphere host requests Report Target Port Groups.
5. The SC Series array responds with new ALUA state changes.
6. vSphere begins Round Robin I/O over new optimal paths.
Note: The Unit Attention Check Condition can be observed in /var/log/vmkernel.log in the following
example. For more information, see the VMware KB article, Interpreting SCSI sense codes in VMware ESXi
and ESX (289902).
2018-02-28T16:59:02.589Z cpu18:66287)NMP: nmp_ThrottleLogForDevice:3617: Cmd
0x28 (0x439500e6bdc0, 111979) to dev "naa.6000d31000ed1f000000000000000015" on
path "vmhba3:C0:T15:L1" Failed: H:0x0 D:0x2 P:0x0 Valid sense data: 0x6 0x2a
0x6. Act:FAILOVER
During extensive testing, it was discovered that vSphere did not consistently or reliably begin using the new
optimal primary Live Volume paths immediately after a role swap as designed. Instead, up to five minutes
elapsed before vSphere recognized the ALUA path state change. This means that vSphere may continue to
follow the Round Robin policy over the non-optimal paths to the secondary Live Volume for up to five minutes.
Dell Technologies is working with VMware to understand this behavior.