Disk Access Across the SAN Fabric

-

 Disk Access / Storage access process occurs when the server is powered on which is connected to SAN fabric. The main components involved at the higher level are Server, SAN Switches, and Storage Array.  Successful completion of the above process will create a link between Server and Storage, which helps in disk access.


The steps involved in as follows

FLOGI - Fabric LOGIn process :

When the server Host Bus Adapter(HBA) power on, it will send its WWNN and WWPN. Using the details shared by the server HBA the switch will assign FCID(Fibre Channel ID) to each HBA and is stored in an internal database. This FCID is used in routing the host request to its storage. This FCID is equivalent to an IP address in the host. 


FC NAme Service:

Once the FCID is allocated by the initial switch connected to Server in the fabric, will now share this information with all other switches in the same fabric. The database within the switch which stores the FCID to WWN mapping is called the FCNS database. With this now all other switches in the same fabric know where to route the read/write request from Storage/Server.

the switch command "show fcns database" can be used to display the information stored in the FCNS database.



PLOGI  :

PLOGI is the process of initializing the device port on the switch and port registration in the Name Server. The switch port facing the end node is called "F port" and the end device port is called "N port".The port connected between the switch is called the "E port". With this, the switch now determines whether the end device is a switch/server/storage and port speed. Before this a proper zoning has to be created between the server and storage,


PRLI - PRocess LogIn:

Process  Login is the Process of establishing communication between the two "N port" i.e., during this process the server sends a PRLI request to Storage. If zoning and masking are configured properly then a communication link is created between the storage and server.


This completes the brief description of the server login process to the fabric. See you all in the next blog.........:-)



Comments

Post a Comment

Popular posts from this blog

PostgreSQL Write-Ahead-Logging(WAL) Archiving Functionality

-
Image
 To recover from PostgreSQL Database crashes Postgres provides WAL archiving functionality from which a standby database can be created by replaying the WAL logs in the recovery site.This interm helps in recovering the database to a particular point in time which is termed as PITR(Point-In-Time_Recovery). WAL files contain the transaction logs from which the database operation can be replayed.Whenever a database operation is triggered a WAL record is created first and then the corresponding data is flushed to disk. In case of any crash, the lost data is recreated by replaying the WAL record. To enable WAL recovering below configuration needs to be configured in postgresql.conf file
Read more

Database Emergency Exit from unforeseen Disasters

-
Image
 With the emerging transformation in the field of AI(Artificial Intelligence) and ML(Machine Learning), data plays a very important role because it allows organizations to store large amounts of business data and retrieve them to get insight into products and customers, which will drive the business. The DataBase helps in accomplishing this. Database Management system provides facilities to access and modify these data efficiently and effectively. Database are very important because of following reasons, Databases enable businesses to efficiently and neatly store and handle massive volumes of data. This facilitates the retrieval and access of particular information when needed. Organizations can use databases to evaluate and interpret their data . Through the utilization of tools like pivot tables and SQL queries, organizations can acquire valuable insights into patterns, trends, and other significant data that can assist in making informed decisions. Through the provision of securit
Read more

RCU Kernel Implementation

-
Image
In our last session, we learned how to use RCU API as a synchronization mechanism using a sample driver. Please visit the  last session  if you missed. In this blog, we will be going through Kernel Implementation of RCU API. The below diagram depicts the overall RCU API used for synchronization. rcu_read_lock() -  The kernel implementation is as follows - static inline void rcu_read_lock(void) {         __rcu_read_lock();         __acquire(RCU);         rcu_lock_acquire(&rcu_lock_map);         rcu_lockdep_assert(rcu_is_watching(),                            "rcu_read_lock() used illegally while idle"); } Basically the above function disables the preemption on the particular cpu on which it is running. So that no other process can preempt this process and the process completes its execution without interruption. After holding rcu_read_lock() it is illegal for the process to explicitly call sleep. rcu_read_unlock()- static inline void rcu_read_unlock
Read more