Interesting possibilities of storage systems HP 3PAR. Part 1 - Persistent Ports
Today I will describe a very interesting, in my opinion, new HP 3PAR storage system feature. Her name is Persistent Ports (virtual ports).
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It is a well-known fact that all manufacturers of data storage systems in a tough competition are constantly forced to add new functions to the microcodes of their storage systems and, of course, correct errors in microcodes. Storage administrators have to update microcodes at regular intervals. Sometimes there is a bug in the firmware, sometimes they want to get new functionality or remove the limitations of the previous version, and often there is a need for migration, because the storage firmware is so old that it is about to be removed from support.
The able hands will always solve the problem of updating the microcode, but there is one problem - the business and its requirements that the service is provided 24 hours, 7 days a week and 365 days a year. And the downtime is only planned and short, and better without them at all. The availability ratio of equipment with a large number of nines must be worked out.
So, solving the problem of eliminating the need for temporary equipment downtime during servicing of storage systems, 3PAR engineers implemented an algorithm called Persistent Ports. The solution impresses with its ingenious simplicity. But before describing this solution, let us recall what needed to be done using other storage systems for this. Further in the text, we mean the data storage systems connected via the FC protocol and updates that do not require simultaneous restarting of all storage system controllers (offline upgrade), since in this case, to completely avoid even the slightest downtime is simply not possible. We consider only the cases in which an alternate restart of the storage controllers is necessary.
The classic solution to this problem is to use software to switch paths on the server (multipath software). In this case, each volume from the storage system must be visible on the server through several independent paths. Paths must go through different storage network switches and different storage controllers.
This scheme is beautiful and works most often with responsible implementation. Multipath-inga software does its job, but sometimes everything is broken about the harsh reality. Reality tells me that:
1. When I see several hundred servers, each of which runs under its own operating system, is administered by its system administrator with an unknown qualification, then I don’t have any desire to check if all of them will switch paths during the upgrade of the storage microcode.
2. I know cases of errors in the software multipath-ing. I mean not the errors in the settings made by the system administrator, but errors in the software. Unfortunately, both of these cases were detected on productive systems. Manufacturers of this software subsequently released patches, but to whom this is easier. Therefore, once again to check on the productive system whether this method will work or whether desire is not enough.
With the next update of 3PAR OS to version 3.1.2, a very useful feature Persistent Ports (also known as virtual ports) appeared. The meaning of this function is that each host port of the storage controller is assigned a partner port on another storage controller. That is, when updating the microcode on one storage system controller, the addresses (wwn) of this controller will be transferred to the working controller. At the same time, the software on the host will not mark any path to the storage system as offline, that is, for multipath-ing software, this operation is transparent.
This feature is now activated by default and manifests itself when the storage controller is restarted and the microcode is updated online. This feature is implemented using NPIV functionality (N_Port ID Virtualization). Let me remind you that NPIV allows several nodes of a storage area network to use access to the network through one physical port, but each has its own unique address (wwn).
')
It is a well-known fact that all manufacturers of data storage systems in a tough competition are constantly forced to add new functions to the microcodes of their storage systems and, of course, correct errors in microcodes. Storage administrators have to update microcodes at regular intervals. Sometimes there is a bug in the firmware, sometimes they want to get new functionality or remove the limitations of the previous version, and often there is a need for migration, because the storage firmware is so old that it is about to be removed from support.
The able hands will always solve the problem of updating the microcode, but there is one problem - the business and its requirements that the service is provided 24 hours, 7 days a week and 365 days a year. And the downtime is only planned and short, and better without them at all. The availability ratio of equipment with a large number of nines must be worked out.
So, solving the problem of eliminating the need for temporary equipment downtime during servicing of storage systems, 3PAR engineers implemented an algorithm called Persistent Ports. The solution impresses with its ingenious simplicity. But before describing this solution, let us recall what needed to be done using other storage systems for this. Further in the text, we mean the data storage systems connected via the FC protocol and updates that do not require simultaneous restarting of all storage system controllers (offline upgrade), since in this case, to completely avoid even the slightest downtime is simply not possible. We consider only the cases in which an alternate restart of the storage controllers is necessary.
The classic solution to this problem is to use software to switch paths on the server (multipath software). In this case, each volume from the storage system must be visible on the server through several independent paths. Paths must go through different storage network switches and different storage controllers.
This scheme is beautiful and works most often with responsible implementation. Multipath-inga software does its job, but sometimes everything is broken about the harsh reality. Reality tells me that:
1. When I see several hundred servers, each of which runs under its own operating system, is administered by its system administrator with an unknown qualification, then I don’t have any desire to check if all of them will switch paths during the upgrade of the storage microcode.
2. I know cases of errors in the software multipath-ing. I mean not the errors in the settings made by the system administrator, but errors in the software. Unfortunately, both of these cases were detected on productive systems. Manufacturers of this software subsequently released patches, but to whom this is easier. Therefore, once again to check on the productive system whether this method will work or whether desire is not enough.
With the next update of 3PAR OS to version 3.1.2, a very useful feature Persistent Ports (also known as virtual ports) appeared. The meaning of this function is that each host port of the storage controller is assigned a partner port on another storage controller. That is, when updating the microcode on one storage system controller, the addresses (wwn) of this controller will be transferred to the working controller. At the same time, the software on the host will not mark any path to the storage system as offline, that is, for multipath-ing software, this operation is transparent.
This feature is now activated by default and manifests itself when the storage controller is restarted and the microcode is updated online. This feature is implemented using NPIV functionality (N_Port ID Virtualization). Let me remind you that NPIV allows several nodes of a storage area network to use access to the network through one physical port, but each has its own unique address (wwn).
Source: https://habr.com/ru/post/168061/
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