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Setting up LVM volumes on a mdraid array

Setting up mdraid array $ mdadm --create /dev/md0 --name=mdvol --level=raid0 --raid-devices=2 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme4n1 mdadm: Defaulting to version 1.2 metadata mdadm: a...

Linux Software RAID

What is RAID? RAID stands for either Redundant Array of Independent Disks, or Redundant Array of Inexpensive Disks. The intention of RAID is to spread your data across several disks, such that a s...

RAID - Redundant Array of Inexpensive Disks

RAID stands for Redundant Array of Inexpensive (Independent) Disks. On most situations you will be using one of the following four levels of RAIDs. RAID 0 RAID 1 RAID 5(6) RAID 10 (also k...

Upgrade kernel version in centos 7

Before upgrade $ cat /etc/centos-release CentOS Linux release 7.4.1708 (Core) $ uname -r 3.10.0-693.el7.x86_64 $ cat /boot/grub2/grubenv saved_entry=CentOS Linux (3.10.0-693.el7.x86_64) 7 (Core)...

Migrate docker data to different directory

This post guides us how to migrate the docker data from the existing directory to a target directory in the case that the old directory runs out of space. Stop the docker daemon $ cat /etc/centos...

Using gstack for docker container process

In a Docker container environment, we won’t get a valid stack trace directly on the container host as below. $ ps -ef |grep smbd root 171118 167977 0 Apr22 ? 00:00:02 /usr/sbin/smbd -...

Network bonding

Introduction Network bonding enables the combination of two or more network interfaces into a single-bonded (logical) interface, which increases the bandwidth and provides redundancy. If a specifi...

Enable ssh passwordless login

Install sshpass package To install sshpass package on the source server from which to enable ssh passwordless login to remote servers: -bash-4.2# rpm -ivh sshpass-1.06-1.el7.x86_64.rpm Enable s...

Tuning kernel parameters in Docker

Configure namespaced kernel parameters(sysctl) at runtime The –sysctl sets namespaced kernel parameters (sysctls) in the container. For example, to turn on IP forwarding in the containers network ...

Sorting algorithm

In this post, it includes the following sorting algorithms. The code is self explained. selection sort insert sort bubble sort quick sort merge sort import java.util.Arrays; public c...

Thread synchronization

Mutexes A mutex is basically a lock that we set (lock) before accessing a shared resource and release (unlock) when we’re done. While it is set, any other thread that tries to set it will block un...

Interprocess communication(IPC)

Pipes Pipes are the oldest form of UNIX System IPC and are provided by all UNIX systems. Pipes have two limitations. Historically, they have been half duplex (i.e., data flows in only one dire...

Using bcc-tools for dynamic kernel tracing

In Red Hat Enterprise Linux 8.1, Red Hat ships a set of fully supported on x86_64 dynamic kernel tracing tools, called bcc-tools, that make use of a kernel technology called extended Berkeley Packe...

blktrace - A block layer IO tracing utility

What can blktrace do? Let’s dive into the block device layer and see how the I/O are handled in disk queues. The following stack shows the I/O paths including the block device layer. The applicat...

Understanding await in iostat

What’s meaning of await in iostat? The following is the description provided for await field in iostat man page. $ man iostat await The average time (in milliseconds) for I/O requests issued ...

Buffered and Direct IO

Buffered and Direct I/O The VxFS responds with read-ahead for sequential read I/O. This results in buffered I/O. The data is prefetched and retained in buffers, in anticipation of application aski...

Network ring buffer

Introduction Receive ring buffers are shared between the device driver and NIC. The card assigns a transmit (TX) and receive (RX) ring buffer. As the name implies, the ring buffer is a circular bu...

Semaphore

What is semaphore A semaphore is a very relaxed type of lockable object. A given semaphore has a predefined maximum count, and a current count. You take ownership of a semaphore with a wait operat...

Max open files limit

System wide open files limit To check system wide files limit: $ cat /proc/sys/fs/file-max 4875932 $ sysctl -a | grep file-max fs.file-max = 4875932 To change system wide files limit: $ echo "...

Iozone - A filesystem benchmark tool

Introduction IOzone is a filesystem benchmark tool. The benchmark generates and measures a variety of file operations. Iozone is useful for performing a broad filesystem analysis of a vendor’s co...