Could someone explain to me (dummy style)
What trespassing is( when it comes to active/active paths)?
Why it matters?
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anyone?
I take it we are discussing SAS controllers?
we’re talking SAN fabrics and how multipath software logs into fibre targets on the storage array and I/O is routed to them.
EMC?
Generally a LUN in a trespass state simply means the LUN is currently owned by the SP that isn’t it’s default owner.
Generally it’s not an issue in Active/Active solutions, but it could be indicative of a problem with one of the controllers.
Yes.
They had a configurable failover mode on the old VNX series, but the latest unity array my work has defaults (and you cannot change it) to failover mode 4 (alua)
But on the previous VNX array they recommended failover mode 3 for AIX / IBM VIOs.
I’ve heard of situations where the primary controller’s battery was going bad, and it caused this to happen.
Fail-over mode 3 is Active/Passive yes?
Thanks for the conv. thus far.
I’ll check the documents on monday. I dont feel like logging into work right now.
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Failover Mode differences:
Failover Mode 3 Passive Always Ready Mode
In this mode of operation the non-owning SP will report that all non-owned LUNs exist and are available for access. Any I/O requests sent to the Non-owning SP will be rejected. This is similar to Failover Mode 1. However, any Test Unit Ready command sent from the server will return with a success message, even to the non-owning SP.
Note: This mode is only used on AIX servers under very specific configuration parameters and has been developed to better handle a CLARiiON non-disruptive upgrade (NDU) when AIX servers are attached.
Failover mode 4
In “failovermode 4,” both storage processors (SPs) will report that all non-owned units exist and are available for access (Inquiry Peripheral Qualifier code 0x00). If the SP is in the process of shutting down, an Inquiry Peripheral Qualifier code of 0x01 will be returned.
In addition, both SPs will accept and process media access commands to the logical unit. Internally, the logical unit is still owned by one of the SPs. The non-owning SP will internally forward the media access operation to the owning SP for processing. As a result, the array operates in what is termed an Asymmetric Logical Unit Access (ALUA) mode of operation. The owning SP will process commands more quickly and efficiently and is thus referred to as the optimized path. The non-owning SP will process commands less quickly and efficiently and is thus referred to as the non-optimized path.
The optimized path is driven by LUN ownership, which can be changed in one of four ways in Active/Active mode:
Explicit Trespass via Navisphere array management command.
Explicit Trespass via Mode Select (Trespass Page) SCSI command.
Explicit Trespass via Set Target Port Group SCSI command.
Implicit Trespass (within the array) if the I/O load on the non-optimized path exceeds the I/O load on the optimized path by a specified quantity of I/O. If IOPS on non-optimal path to a LUN exceed IOPS by 128k via the optimal path , CLARiiON FLARE code will perform implicit trespass of the LUN.
The Auto-trespass setting of the logical unit is ignored in this mode of operation.