Linux For You Mate ...

Many times for the testing purpose you need to create big capacity dummy files on the filesystems to check few features of disks/arrays or some kind of drivers. So here I will show you how you can create such a big file and also depending on your requirement if you need just an empty file or you need to zero it out, means writing zero's on it. ESXi server has a inbuilt utility which makes this task easier, named "vmkfstool". This is the same utility which is also used for making new VMDK files for the VM's, and that's what we will be using for testing purpose: Create 50GB large empty file: # vmkfstools -c 50G /vmfs/volumes/esx_ds/dummy-fill/fill1.vmdk -d thin Create: 100% done. Create 50GB large file with zero's written on it: # vmkfstools -c 50G /vmfs/volumes/esx_ds/dummy-fill/fill1.vmdk -d eagerzeroedthick Creating disk '/vmfs/volumes/esx_ds/dummy-fill/fill1.vmdk' and zeroing it out... Create: 100% done. [root@CRT3-D-ESX6U3:~] ls -l...

Many times for the testing purpose you need to create big capacity dummy files on the filesystems to check few features of disks/arrays or some kind of drivers. So here I will show you how you can create such a big file and also depending on your requirement if you need just an empty file or you need to zero it out, means writing zero's on it. To create an empty 50GB file using dd utility: # dd if=/dev/zero of=/dummy-fill/dummy_file.img bs=1 count=0 seek= 50G 0+0 records in 0+0 records out 0 bytes (0 B) copied, 0.00042393 s, 0.0 kB/s Here above command will create 50GB of the file named " dummy_file.img " inside " /dummy-fill/ " folder. Where "53687091200" is in Bytes which is equivalent to 50GB. To create a big 50GB file and to write zero's on it follow below commands; # dd if=/dev/zero of=/dummy-fill/ dummy_file.img  count=1024 bs=52428800 1024+0 records in 1024+0 records out 53687091200 bytes (50 GB) copied, 58.52256 s, 426 MB/...

Many times for the testing purpose you need to create big capacity dummy files on the filesystems to check few features of disks/arrays or some kind of drivers. So here I will show you how you can create such a big file and also depending on your requirement if you need just an empty file or you need to zero it out, means writing zero's on it. To create an empty 50GB file using Powershell: PS C:\>   fsutil file createnew d:\dummy_file.img 53687091200 Here above command will create 50GB of the file named "dummy_file.img" inside "D:" filesystem. Where " 53687091200 " is in Bytes which is equivalent to 50GB. To create a big 50GB file and to write zero's on it follow below commands; Creates a new file of a specified size: PS C:\> fsutil file createnew  d:\dummy_file.img  53687091200 File d:\fill1 is created Set the valid data length for a file: PS C:\> fsutil file setvaliddata d:\ dummy_file.img  53687091200 Valid data le...

A kernel is the core of an Operating System. It provides basic services for all other components of the OS. It is the main layer between the OS and hardware, and it helps with process and memory management, file systems, device control, and networking. Following is Linux  Kernel Architecture : User Space is the memory area where all user mode applications works and this memory can be swapped out when needed. Userspace process normally runs in its own virtual memory space and unless explicitly requested, cannot access the memory of other processes. Due to the protection afforded by this sort of isolation, crashes in user mode are always recoverable. Kernel Space is strictly reserved for running the kernel, OS background process, kernel extensions and device drivers. In Linux kernel space gives full access to the hardware, although some extensions runs in the user space. Crashes in kernel mode are catastrophic; they will halt the entire PC. These two modes are enforced...

Zoning is an Fibre Channel switch function that enables node ports within the fabric to be logically segmented into groups and communicate with each other within the group. If zoning is not configured, the fabric controller sends an RSCN to all the nodes in the fabric. Involving the nodes that are not impacted by the change results in increased fabric-management traffic. Zoning also provides access control, along with other access control mechanisms, such as LUN masking. Zoning provides control by allowing only the members in the same zone to establish communication with each other. Types of Zoning: Port zoning : Uses the physical address of switch ports to define zones. In port zoning, access to node is determined by the physical switch port to which a node is connected. The zone members are the port identifier (switch domain ID and port number) to which HBA and its targets (storage devices) are connected. If a node is moved to another switch port in the fabric, port zoning mu...

Fabric services have three login types as explained below: FLOGI also known as Fabric Login . Performed between a N_Port and a F_Port. To log on to the fabric, a node sends a FLOGI frame with the WWNN and WWPN parameters to the login service at the pre-defined FC address FFFFFE (Fabric Login Server). In turn, the switch accepts the login and returns an Accept (ACC) frame with the assigned FC address for the node. Immediately after the FLOGI, the N_Port registers itself with the local Name Server on the switch, indicating its WWNN, WWPN, port type, class of service, assigned FC address and so on. After the N_Porth as logged in, it can query the name server database for information about all other logged in ports. PLOGI also known as Port Login . Performed between two N_Ports to establish a session. The initiator N_Portsends a PLOGI request frame to the target N_Port, which accepts it. The target N_Port returns an ACC to the initiator N_Port. Next, the N_Ports exchange service par...

Fibre Channel switches, regardless of the manufacturer, provide a common set of services as defined in the Fibre Channel standards. These services are available at certain pre-defined addresses. Some of these services are Fabric Login Server, Fabric Controller, Name Server, and Management Server. The Fabric Login Server is located at the predefined address of FFFFFE and is used during the initial part of the node’s fabric login process. The Name Server (also known as Distributed Name Server) is located at the predefined address FFFFFC and is responsible for name registration and management of node ports. Each switch exchanges its Name Server information with other switches in the fabric to maintain a synchronized, distributed name service. Fabric Controller located at the predefined address FFFFFD . The Fabric Controller provides services to both node ports and other switches. The Fabric Controller is responsible for managing and distributing Registered State Change Notific...

It is easier to understand a communication protocol by viewing it as a structure of independent layers. Fibre Channel Protocol defines the communication protocol in five layers: FC-0 through FC-4 (except FC-3 layer, which is not implemented). FC-0 Layer is the lowest layer in the Fibre Channel Protocol stack. This layer defines the physical interface, media, and transmission of bits. The FC-0 specification includes cables, connectors, and optical and electrical parameters for a variety of data rates. The Fibre Channel transmission can use both electrical and optical media. FC-1 Layer defines how data is encoded prior to transmission and decoded upon receipt. At the transmitter node, an 8-bit character is encoded into a 10-bit transmission character. This character is then transmitted to the receiver node. At the receiver node, the 10-bit character is passed to the FC-1 layer, which decodes the 10-bit character into the original 8-bit character. Fibre Channel links ...

Ports reserved in a switched fabric can be one of the following types: N_Port is an endpoint in the fabric. This port is also known as the node port. Typically, it is a host port (HBA) or a storage array port that is connected to a switch in a switched fabric. E_Port is a port that forms the connection between two FC switches. This port is also known as the expansion port. The E_Port on an FC switch connects to the E_Port of another FC switch in the fabric ISLs. F_Port is a port on a switch that connects to a N_Port, which is also known as a fabric port. G_Port is a   generic port on a switch that can operate as an E_Port or a F_Port and determines its functionality automatically during initialization.

One of the basic features of the Linux kernel is that it abstracts the handling of devices. All hardware devices look like regular files; they can be opened, closed, read and written using the same, standard, system calls that are used to manipulate files. Every device in the system is represented by a file. For block (disk) and character devices, these device files are created by the mknod command and they describe the device using major and minor device numbers. The kernel needs to be told how to access the device. Not only does the kernel need to be told what kind of device is being accessed but also any special information, such as the partition number if it's a hard disk or density if it's a floppy, for example. This is accomplished by the major number and minor number of that device. Major Numbers : All devices controlled by the same device driver have a common major device number. The major number is actually the offset into the kernel's device driver table, whi...

Hot-plugging (which is the word used to describe the process of inserting devices into a running system) is achieved in a Linux distribution by a combination of three components: Udev, HAL, and Dbus . Udev is a userspace daemon, that supplies a dynamic device directory containing only the nodes for devices which are connected to the system. It creates or removes the device node files in the /dev directory as they are plugged in or taken out. Dbus is like a system bus which is used for inter-process communication. The HAL gets information from the Udev service, when a device is attached to the system and it creates an XML representation of that device. It then notifies the corresponding desktop application like Nautilus through the Dbus and Nautilus will open the mounted device files. Dbus is an IPC mechanism, which allows applications to register for system device events. Udev is the device manager for the Linux 2.6 kernel that creates/removes device nodes in...