Tips for implementing NPIV on IBM Power Systems
Virtual Fibre Channel with Virtual I/O and AIX 6.1
Overview
In this article, I will share with you my experience in implementing NPIV on IBM Power Systems with AIX and the Virtual I/O Server (VIOS). There are several publications that already discuss the steps on how to configure NPIV using a VIOS, and I have provided links to some of these in the resources section. Therefore, I will not step through the process of creating virtual Fibre Channel (FC) adapters or preparing your environment so that it is NPIV and virtual FC ready. I assume you already know about this and will ensure you have everything you need. Rather, I will impart information that I found interesting and perhaps undocumented during my own real-life experience of deploying this technology. Ultimately this system was to provide an infrastructure platform to host SAP applications running against a DB2 database.
NPIV (N_Port ID Virtualization) is an industry standard that allows a single physical Fibre Channel port to be shared among multiple systems. Using this technology you can connect multiple systems (in my case AIX LPARs) to one physical port of a physical fibre channel adapter. Each system (LPAR) has its own unique worldwide port name (WWPN) associated with its own virtual FC adapter. This means you can connect each LPAR to physical storage on a SAN natively.
This is advantageous for several reasons. First, you can save money. Having the ability to share a single fibre channel adapter among multiple LPARs could save you the cost of purchasing more adapters than you really need.
Another reason to use NPIV is the reduction in VIOS administration overhead. Unlike virtual SCSI (VSCSI), there is no need to assign the SAN disks to the VIOS first and then map them to the Virtual I/O client (VIOC) LPARs. Instead, the storage is zoned directly to the WWPNs of the virtual FC adapters on the clients. It also eliminates the need to keep your documentation up to date every time you map a new disk to an LPAR/VIOS or un-map a disk on the VIO server.
I/O performance is another reason you may choose NPIV over VSCSI. With NPIV all paths to a disk can be active with MPIO, thus increasing the overall bandwidth and availability to your SAN storage. The I/O load can be load-balanced across more than one VIO server at a time. There is no longer any need to modify a clients VSCSI hdisk path priority to send I/O to an alternate VIO server, as all I/O can be served by all the VIO servers if you wish.
One more reason is the use of disk “copy service” functions. Most modern storage devices provide customers with the capability to “flash copy” or “snap shot” their SAN LUNs for all sorts of purposes, like cloning of systems, taking backups, and so on. It can be a challenge to implement these types of functions when using VSCSI. It is possible, but automation of the processes can be tricky. Some products provide tools that can be run from the host level rather than on the storage subsystem. For this to work effectively, the client LPARs often need to “see” the disk as a native device. For example, it may be necessary for an AIX system to detect that its disk is a native NetApp disk for the NetApp “snapshot” tools to work. If it cannot find a native NetApp device, and instead finds only a VSCSI disk, and it is unable to communicate with the NetApp system directly, then the tool may fail to function or be supported.
The biggest disadvantage (that I can see) to using NPIV is the fact that you must install any necessary MPIO device drivers and/or host attachment kits on any and all of the client LPARs. This means that if you have 100 AIX LPARs that all use NPIV and connect to IBM DS8300 disk, you must install and maintain SDDPCM on all 100 LPARs. In contrast, when you implement VSCSI, the VIOS is the only place that you must install and maintain SDDPCM. And there’s bound to be fewer VIOS than there are clients! There are commonly only two to four VIO servers on a given Power system.
Generally speaking, I’d recommend NPIV at most large enterprise sites since it is far more flexible, manageable, and scalable. However, there’s still a place for VSCSI, even in the larger sites. In some cases, it may be better to use VSCSI for the rootvg disk(s) and use NPIV for all non-rootvg (data) volume groups. For example, if you boot from SAN using NPIV (rootvg resides on SAN disk) and you had to install MPIO device drivers to support the storage. It can often be difficult to update MPIO software when it is still in use, which in the case of SAN boot is all the time. There are procedures and methods to work around this, but if you can avoid it, then you should consider it!
For example, if you were a customer that had a large number of AIX LPARs that were all going to boot from HDS SAN storage, then I’d suggest that you use VSCSI for the rootvg disks. This means that HDLM (Hitachi Dynamic Link Manager, HDS MPIO) software would need to be installed on the VIOS, the HDS LUNs for rootvg would be assigned to and mapped from the VIOS. All other LUNS for data (for databases or application files/code) would reside on storage presented via NPIV and virtual FC adapters. HDLM would also be installed on the LPARs but only for non-rootvg disks. Implementing it this way means that when it comes time to update the HDLM software on the AIX LPARs, you would not need to worry about moving rootvg to non-HDS storage so that you can update the software. Food for thought!
Environment
The environment I will describe for my NPIV implementation consists of a POWER7 750 and IBM XIV storage. The client LPARs are all running AIX 6.1 TL6 SP3. The VIO servers are running version 2.2.0.10 Fix Pack 24 Service Pack 1 (2.2.0.10-FP-24-SP-01). The 750 is configured with six 8GB fibre channel adapters (feature code 5735). Each 8GB FC adapter has 2 ports. The VIO servers were assigned 3 FC adapters each. The first two adapters in each VIOS would be used for disk and the last FC adapter in each VIOS would be for tape connectivity.
NPIV and virtual FC for disk
I made the conscious decision during the planning stage to provide each production LPAR with four virtual FC adapters. The first two virtual FC adapters would be mapped to the first two physical FC ports on the first VIOS and the last two virtual FC adapters would be mapped to first two physical FC ports on the second VIOS. As shown in the following diagram below.
Figure 1: Virtual FC connectivity to SAN and Storage
I also decided to isolate other disk traffic (for example, non-critical production traffic) over different physical FC adapters/ports. In the previous diagram, the blue lines/LUNs indicate production traffic. This traffic is mapped from the virtual adapters, fcs0 and fcs1 in an LPAR, to the physical ports on the first FC adapters in vio1: fcs0 and fcs1. The virtual FC adapters, fcs2 and fcs3 in an LPAR, map to the physical ports on the first FC adapter in vio2: fcs0 and fcs1.
The red lines indicate all non-critical disk traffic. For example, the NIM and Tivoli Storage Manager LPARs use different FC adapters in each VIOS than the production LPARs. The virtual FC adapters, fcs0 and fcs1, map to the physical ports on the second FC adapter, fcs2 and fcs3 in vio1. The virtual FC adapters, fcs2 and fcs3, map to the physical ports on the second FC adapter, fcs2 and fcs3 in vio2.
An example of the vfcmap commands that we used to create this mapping on the VIO servers are shown here:
For production systems (e.g. LPAR4):
- Map LPAR4 vfchost0 adapter to physical FC adapter fcs0 on vio1.
- Map LPAR4 vfchost1 adapter to physical FC adapter fcs1 on vio1.
- Map LPAR4 vfchost0 adapter to physical FC adapter fcs0 on vio2.
- Map LPAR4 vfchost1 adapter to physical FC adapter fcs1 on vio2.
For non-critical systems (e.g. NIM1):
- Map NIM1 vfchost3 adapter to physical FC adapter fcs2 on vio1.
- Map NIM1 vfchost4 adapter to physical FC adapter fcs3 on vio1.
- Map NIM1 vfchost3 adapter to physical FC adapter fcs2 on vio2.
- Map NIM1 vfchost4 adapter to physical FC adapter fcs3 on vio2.
I used the lsmap –all –npiv
command on each of the VIO servers to confirm that the mapping of the
vfchost adapters, to the physical FC ports, was correct (as shown
below).
vio1 (production LPAR):
vio1 (non-production LPAR):
vio2 (production LPAR):
vio2 (non-production LPAR):
Fortunately, as we were using IBM XIV storage, we did not need to install additional MPIO devices drivers to support the disk. AIX supports XIV storage natively. We did, however, install some additional management utilities from the XIV host attachment package. This gave us handy tools such as xiv_devlist (output shown below).
If you are planning on implementing XIV storage with AIX, I highly recommend that you take a close look at Anthony Vandewert’s blog on this topic.
You may have noticed in the diagram that the VIO servers themselves boot from internal SAS drives in the 750. Each VIO server was configured with two SAS drives and a mirrored rootvg. They did not boot from SAN.
LPAR profiles
During the build of the LPARs we noticed that if we booted a new LPAR with all four of its virtual FC adapters in place, the fcsX adapter name and slot id were not in order (fcs0=slot32, fcs1=slot33, fcs3=slot30, fcs4=slot31). To prevent this from happening, we created two profiles for each LPAR.
The first profile (known as normal) contained the information for all four of the virtual FC adapters. The second profile (known as wwpns) contained only the first two virtual FC adapters that mapped to the first two physical FC ports on vio1. Using this profile to perform the LPARs first boot and to install AIX allowed the adapters to be discovered in the correct order (fcs0=slot30, fcs1=slot31). After AIX was installed and the LPAR booted, we would then re-activate the LPAR using the normal profile and all four virtual FC adapters.
Two LPAR profiles exist for each AIX LPAR. An example is shown below.
Figure 2: LPAR profiles for virtual FC
The profile named normal contained all of the necessary Virtual I/O devices for an LPAR (shown below). This profile was used to activate an LPAR during standard operation.
Figure 3: Profile with all virtual FC adapters used after install
The profile named wwpns contained only the first two virtual FC devices for an LPAR (shown below). This profile was only used to activate an LPAR in the event that the AIX operating system needed to be reinstalled. Once the AIX installation completed successfully, the LPAR was activated again using the normal profile. This configured the remaining virtual FC adapters.
Figure 4: An LPAR with first two virtual FC adapters only
Also during the build process, we needed to collect a list of WWPNs for the new AIX LPARs we were installing from scratch. There were two ways we could find the WWPN for a virtual Fibre Channel adapter on a new LPAR (for example, one that did not yet have an operating system installed). First, we started by checking the LPAR properties from the HMC (as shown below).
Figure 5: Virtual FC adapter WWPNS
To speed things up we moved to the HMC command line tool, lssyscfg, to display the WWPNs (as shown below).
We now had a list of WWPNs for each LPAR.
We gave these WWPNS to the SAN administrator so that he could manually “zone in” the LPARs on the SAN switches and allocate storage to each. To speed things up even more, we used sed to insert colons into the WWPNs. This allowed the SAN administrator to simply cut and paste the WWPNs without needing to insert colons manually.
An important note here, if you plan on implementing Live Partition Mobility (LPM) with NPIV enabled systems, make sure you zone both of the WWPNs for each virtual FC adapter on the client LPAR. Remember that for each client virtual FC adapter that is created, a pair of WWPNs is generated (a primary and a secondary). Please refer to Live Partition Mobility with Virtual Fibre Channel in the resources section for more information.
Virtual FC adapters for tape
Tivoli Storage Manager was the backup software used to backup and recover the systems in this new environment. Tivoli Storage Manager would use a TS3310 tape library, as well as disk storage pools to backup client data. In this environment, we chose to use virtual FC adapters to connect the tape library to Tivoli Storage Manager. This also gave us the capability to assign the tape devices to any LPAR, without moving the physical adapters from one LPAR to another, should the need arise in the future. As I mentioned earlier, there were three 2-port 8GB FC adapters assigned to each VIOS. Two adapters were used for disk and the third would be used exclusively for tape.
The following diagram shows that physical FC ports, fcs4 and fcs5, in each VIOS would be used for tape connectivity. It also shows that each of the 4 tape drives would be zoned to a specific virtual FC adapter in the Tivoli Storage Manager LPAR.
Figure 6. Tape drive connectivity via virtual FC
The Tivoli Storage Manager LPAR was initially configured with virtual FC adapters for connectivity to XIV disk only. As shown in the lspath output below, fcs0 through fcs3 are used exclusively for access to disk only.
To connect to the tape drives, we configured four additional virtual FC adapters for the LPAR. First, we ensured that the physical adapters were available and had fabric connectivity. On both VIOS, we used the lsnports command to determine the state of the adapters and their NPIV capability. As shown in the following output, the physical adapter’s fcs4 and fcs5 were both available and NPIV ready. There was a 1 in the fabric column. If it was zero then the adapter may not be connected to an NPIV capable SAN.
When I initially checked the state of the adapters on both VIOS, I encountered the following output from lsnports:
As you can see, only the fcs4 adapter was discovered; the fabric value for fcs4 was 0 and fcs5 was missing. Both of these issues were the result of physical connectivity issues to the SAN. The cables were unplugged and/or they had a loopback adapter plugged into the interface. The error report indicated link errors on fcs4 but not for fcs5.
Once the ports were physically connected to the SAN switches, I removed the entry for fcs4 from the ODM (as shown below) and then ran cfgmgr on the VIOS.
Then both fcs4 and fcs5 were discovered and configured correctly.
The Tivoli Storage Manager LPARs dedicated virtual FC adapters, for tape, appeared as fcs4, fcs5, fcs6 and fcs7. The plan was for fcs4 on tsm1 to map to fcs4 on vio1, fcs5 to map to fcs5 on vio1, fcs6 to map to fcs4 on vio2, and fcs7 to map to fcs5 on vio2.
The virtual adapter slot configuration was as follows:
We created two new virtual FC host (vfchost) adapters on vio1 and two new vfchost adapters on vio2. This was done by updating the profile for both VIOS (on the HMC) with the new adapters and then adding them with a DLPAR operation on each VIOS. Once we had run the cfgdev command on each VIOS to bring in the new vfchost adapters, we needed to map them to the physical FC ports.
Using the vfcmap command on each of the VIOS, we mapped the physical ports to the virtual host adapters as follows:
- Map tsm1 vfchost60 adapter to physical FC adapter fcs4 on vio1.
- Map tsm1 vfchost61 adapter to physical FC adapter fcs5 on vio1.
- Map tsm1 vfchost60 adapter to physical FC adapter fcs4 on vio2.
- Map tsm1 vfchost61 adapter to physical FC adapter fcs5 on vio2.
Next we used DLPAR to update the client LPAR with four new virtual FC adapters. Please make sure you read the procedure on adding a virtual FC adapter to client LPAR. If care is not taken, the WWPNs for a client LPAR can be lost, which can result in loss of connectivity to your SAN storage. You may also want to review the HMC’s chsyscfg command, as it is possible to use this command to modify WWPNs for an LPAR.
After running the cfgmgr command on the LPAR, we confirmed we had four new virtual FC adapters. We ensured that we saved the LPARs current configuration, as outlined in the procedure.
On both VIOS, we confirmed that the physical to virtual mapping on the FC adapters was correct using the lsmap –all –npiv command. Also checking that client LPAR had successfully logged into the SAN by noting the Status: LOGGED_IN entry in the lsmap output for each adapter.
We were able to capture the WWPNs for the new adapters at this point. This information was required to zone the tape drives to the system.
The IBM Atape device drivers were installed prior to zoning in the TS3310 tape drives.
Then, once the drives had been zoned to the new WWPNs, we ran cfgmgr on the Tivoli Storage Manager LPAR to configure the tape drives.
Our new tape drives were now available to Tivoli Storage Manager.
Monitoring virtual FC adapters
Apparently the viostat command on the VIO server allows you to monitor I/O traffic on the vfchost adapters (as shown in the following example).
I must admit I had limited success using this tool to monitor I/O on these devices. I am yet to discover why this tool did not report any statistics for any of my vfchost adapters. Perhaps it was an issue with the level of VIOS code we were running?
Fortunately, nmon captures and reports on virtual FC adapter performance statistics on the client LPAR. This is nothing new, as nmon has always captured FC adapter information, but it is good to know that nmon can record the data for both virtual and physical FC adapters.
Figure 7. nmon data for virtual FC adapter usage
The fcstat command can be used on the client LPARs to monitor performance statistics relating to buffer usage and overflows on the adapters. For example, the following output indicated that we needed to tune some of the settings on our virtual FC adapters. In particular the following attributes were modified, num_cmd_elems and max_xfer_size.
We also found buffer issues (via the fcstat command) on the physical adapters on the VIO servers. We tuned the FC adapters on the VIO servers to match the settings on the client LPARs, such as max_xfer_size=0x200000 and num_cmd_elems=2048.
The fcstat command will report a value of UNKNOWN for some attributes of a virtual FC adapter. Because it is a virtual adapter, it does not contain any information relating to the physical adapter attributes, such as firmware level information or supported port speeds.
Conclusion
In all that describes my experience with NPIV, Power Systems, Virtual I/O and AIX. I hope you have enjoyed reading this article. Of course, as they say, “there’s always more than one way to skin a cat“! So please feel free to contact me and share your experiences with this technology, I’d like to hear your thoughts and experiences.