http://www.cyberciti.biz/tips This is a Linux sys admin journal by Vivek about sys admin work, Linux tips & tricks, hacks, news and more. Wed, 24 Apr 2013 18:50:55 +0000 en-US hourly 1 http://wordpress.org/?v=3.5.1 http://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html http://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html#comments Tue, 15 Jun 2010 20:22:30 +0000 nixCraft http://www.cyberciti.biz/tips/?p=7084 It is no secret that I am a pretty big fan of excellent Linux Software RAID. Creating, assembling and rebuilding small array is fine. But, things started to get nasty when you try to rebuild or resync large size array. You may get frustrated when you see it is going to take 22 hours to rebuild the array. You can always increase RAID resync performance using the following technique. ]]> http://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html/feed 35 http://www.cyberciti.biz/tips/vmware-add-a-new-hard-disk-without-rebooting-guest.html http://www.cyberciti.biz/tips/vmware-add-a-new-hard-disk-without-rebooting-guest.html#comments Sat, 18 Jul 2009 06:55:53 +0000 nixCraft /sys/class/scsi_host/host#/scan]]> http://www.cyberciti.biz/tips/?p=5411 As a system admin, I need to use additional hard drives for to provide more storage space or to separate system data from user data. This procedure, adding physical block devices to virtualized guests, describes how to add a hard drive on the host to a virtualized guest using VMWare software running Linux as guest.

It is possible to add or remove a SCSI device explicitly, or to re-scan an entire SCSI bus without rebooting a running Linux VM guest. This how to is tested under Vmware Server and Vmware Workstation v6.0 (but should work with older version too). All instructions are tested on RHEL, Fedora, CentOS and Ubuntu Linux guest / hosts operating systems. ]]> http://www.cyberciti.biz/tips/vmware-add-a-new-hard-disk-without-rebooting-guest.html/feed 34 http://www.cyberciti.biz/tips/raid-hardware-vs-raid-software.html http://www.cyberciti.biz/tips/raid-hardware-vs-raid-software.html#comments Tue, 07 Jul 2009 16:01:56 +0000 nixCraft http://www.cyberciti.biz/tips/?p=5306 A redundant array of inexpensive disks (RAID) allows high levels of storage reliability. RAID is not a backup solution. It is used to improve disk I/O (performance) and reliability of your server or workstation. A RAID can be deployed using both software and hardware. But the real question is whether you should use a hardware RAID solution or a software RAID solution.]]> http://www.cyberciti.biz/tips/raid-hardware-vs-raid-software.html/feed 29 http://www.cyberciti.biz/tips/top-linux-monitoring-tools.html http://www.cyberciti.biz/tips/top-linux-monitoring-tools.html#comments Sat, 27 Jun 2009 02:26:39 +0000 nixCraft http://www.cyberciti.biz/tips/?p=4934 Need to monitor Linux server performance? Try these built-in command and a few add-on tools. Most Linux distributions are equipped with tons of monitoring. These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem. The commands discussed below are some of the most basic commands when it comes to system analysis and debugging server issues such as:

1. Finding out bottlenecks.
2. Disk (storage) bottlenecks.
3. CPU and memory bottlenecks.
4. Network bottlenecks.

]]> http://www.cyberciti.biz/tips/top-linux-monitoring-tools.html/feed 316 http://www.cyberciti.biz/tips/howto-resize-vmware-virtual-harddisk-size.html http://www.cyberciti.biz/tips/howto-resize-vmware-virtual-harddisk-size.html#comments Tue, 09 Jun 2009 14:22:42 +0000 nixCraft http://www.cyberciti.biz/tips/?p=4998 I've Windows Vista installed as a guest under Ubuntu Linux using VMWARE Workstation 6.0. This is done for testing purpose and browsing a few site that only works with Internet Explorer. Since I only use it for testing I made 16GB for Vista and 5GB for CentOS and 5GB in size for FreeBSD guest operating systems. However, after some time I realized I'm running out of disk space under both CentOS and Vista. Adding a second hard drive under CentOS solved my problem as LVM was already in use. Unfortunately, I needed to double 32GB space without creating a new D: drive under Windows Vista. Here is a simple procedure to increase your Virtual machine's disk capacity by resizing vmware vmdk file.]]> http://www.cyberciti.biz/tips/howto-resize-vmware-virtual-harddisk-size.html/feed 31 http://www.cyberciti.biz/tips/common-causes-of-downtime-in-datacenter.html http://www.cyberciti.biz/tips/common-causes-of-downtime-in-datacenter.html#comments Wed, 27 May 2009 14:42:27 +0000 nixCraft http://www.cyberciti.biz/tips/?p=4895 Unplanned downtime may be the result of a software bug, human error, equipment failure, power failure, and much more. Last week was a bad one. We faced three different downtime:

• First, there was a fiber cut for one of our data center resulting into routing anomalies due BGP reroute. Traffic was rerouted but updating those BGP tables took some time to update.
• Someone from networking team failed to follow proper maintenance procedures for network device resulted into 55 minutes downtime.
• One of our SAN hardware failure - Many internal UNIX / Linux web applications use SAN to store data including file server, tracking apps, R&D apps, IT help desk, LAN and WAN servers failed. This one lasted for 12 hrs. It was stared around midnight. The vendor replaced entire SAN hardware. Now we have dual stacked SAN as a backup device for internal usage.

Note: There is a poll embedded within this post, please visit the site to participate in this post's poll.]]> http://www.cyberciti.biz/tips/common-causes-of-downtime-in-datacenter.html/feed 6 http://www.cyberciti.biz/tips/oracle-to-purchase-sun-microsystems-for-74b.html http://www.cyberciti.biz/tips/oracle-to-purchase-sun-microsystems-for-74b.html#comments Tue, 21 Apr 2009 10:10:39 +0000 nixCraft http://www.cyberciti.biz/tips/?p=4622 Look like combined company will give a tough time to both IBM and HP. Sun Microsystems and Oracle Corporation announced yesterday that they have entered into a definitive agreement under which Oracle will acquire Sun common stock for a total of $7.4 billion or $5.6 billion net of Sun's cash and debt.]]> http://www.cyberciti.biz/tips/oracle-to-purchase-sun-microsystems-for-74b.html/feed 3 http://www.cyberciti.biz/tips/linux-convert-ext3-to-ext4-file-system.html http://www.cyberciti.biz/tips/linux-convert-ext3-to-ext4-file-system.html#comments Fri, 23 Jan 2009 15:45:57 +0000 nixCraft http://www.cyberciti.biz/tips/?p=4348 Some time ago ext4 was released and available for Linux kernel. ext4 provides some additional benefits and perforce over ext3 file system. You can easily convert ext3 to ext4 file system. The next release of Fedora, 11, will default to the ext4 file system unless serious regressions are seen. In this quick tutorial you will learn about converting ext3 to ext4 file system.]]> http://www.cyberciti.biz/tips/linux-convert-ext3-to-ext4-file-system.html/feed 19 http://www.cyberciti.biz/tips/vmware-esx-server-scsi-timeout-for-linux-guest.html http://www.cyberciti.biz/tips/vmware-esx-server-scsi-timeout-for-linux-guest.html#comments Sat, 17 Jan 2009 20:34:23 +0000 nixCraft /sys$DEVPATH/device/timeout'"]]> http://www.cyberciti.biz/tips/?p=5811 Recently, I noticed that the timeout values differ on CentOS v5.x and RHEL Linux 5.x guests on VMWare ESX4 and ESX3.5.]]> http://www.cyberciti.biz/tips/vmware-esx-server-scsi-timeout-for-linux-guest.html/feed 0 http://www.cyberciti.biz/tips/linux-virtualization-software.html http://www.cyberciti.biz/tips/linux-virtualization-software.html#comments Wed, 31 Dec 2008 15:00:59 +0000 nixCraft http://www.cyberciti.biz/tips/?p=4215 Virtualization is the latest buzz word. You may wonder computers are getting cheaper every day, why should I care and why should I use virtualization? Virtualization is a broad term that refers to the abstraction of computer resources such as:

1. Platform Virtualization
2. Resource Virtualization
3. Storage Virtualization
4. Network Virtualization
5. Desktop Virtualization

This article describes why you need virtualization and list commonly used FOSS and proprietary Linux virtualization software. ]]> http://www.cyberciti.biz/tips/linux-virtualization-software.html/feed 27 http://www.cyberciti.biz/tips/howto-linux-boot-2tb-larger-raidarray-harddisk.html http://www.cyberciti.biz/tips/howto-linux-boot-2tb-larger-raidarray-harddisk.html#comments Thu, 04 Dec 2008 07:13:58 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3718 I've already written about creating a partition size larger than 2TB under Linux using GNU parted command with GPT. In this tutorial, I will provide instructions for booting to a flat 2TB or larger RAID array under Linux using the GRUB boot loader.]]> http://www.cyberciti.biz/tips/howto-linux-boot-2tb-larger-raidarray-harddisk.html/feed 3 http://www.cyberciti.biz/tips/linux-swap-space.html http://www.cyberciti.biz/tips/linux-swap-space.html#comments Wed, 19 Nov 2008 08:50:49 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3586 Linux and other Unix-like operating systems use the term "swap" to describe both the act of moving memory pages between RAM and disk, and the region of a disk the pages are stored on. It is common to use a whole partition of a hard disk for swapping. However, with the 2.6 Linux kernel, swap files are just as fast as swap partitions. Now, many admins (both Windows and Linux/UNIX) follow an old rule of thumb that your swap partition should be twice the size of your main system RAM. Let us say I've 32GB RAM, should I set swap space to 64 GB? Is 64 GB of swap space really required? How big should your Linux / UNIX swap space be? ]]> http://www.cyberciti.biz/tips/linux-swap-space.html/feed 64 http://www.cyberciti.biz/tips/disable-caching-on-the-cifs-nfs-client.html http://www.cyberciti.biz/tips/disable-caching-on-the-cifs-nfs-client.html#comments Sun, 16 Nov 2008 09:03:15 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3551 If your network is heavily loaded you may see some problem with Common Internet File System (CIFS) and NFS under Linux. By default Linux CIFS mount command will try to cache files open by the client. You can use mount option forcedirectio when mounting the CIFS filesystem to disable caching on the CIFS client. This is tested with NETAPP and other storage devices and Novell, CentOS, UNIX and Red Hat Linux systems. This is the only way to avoid data mis-compare and problems.]]> http://www.cyberciti.biz/tips/disable-caching-on-the-cifs-nfs-client.html/feed 2 http://www.cyberciti.biz/tips/linux-unix-parallel-nfs.html http://www.cyberciti.biz/tips/linux-unix-parallel-nfs.html#comments Thu, 13 Nov 2008 12:17:31 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3519 NFS is pretty old file sharing technology for UNIX based system and storage systems. However, it suffers from performance issues. NFSv4.1 address data access issues by adding a new feature called parallel NFS (pNFS) - a method of introducing Data Access Parallelism. The end result is ultra fast file sharing for clusters and high availability configurations.

The Network File System (NFS) is a stalwart component of most modern local area networks (LANs). But NFS is inadequate for the demanding input- and output-intensive applications commonly found in high-performance computing -- or, at least it was. The newest revision of the NFS standard includes Parallel NFS (pNFS), a parallelized implementation of file sharing that multiplies transfer rates by orders of magnitude. ]]> http://www.cyberciti.biz/tips/linux-unix-parallel-nfs.html/feed 2 http://www.cyberciti.biz/tips/howto-setup-linux-iscsi-target-sanwith-tgt.html http://www.cyberciti.biz/tips/howto-setup-linux-iscsi-target-sanwith-tgt.html#comments Tue, 11 Nov 2008 02:39:48 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3485 Linux target framework (tgt) aims to simplify various SCSI target driver (iSCSI, Fibre Channel, SRP, etc) creation and maintenance. The key goals are the clean integration into the scsi-mid layer and implementing a great portion of tgt in user space.
The developer of IET is also helping to develop Linux SCSI target framework (stgt) which looks like it might lead to an iSCSI target implementation with an upstream kernel component. iSCSI Target can be useful:

a] To setup stateless server / client (used in diskless setups).
b] Share disks and tape drives with remote client over LAN, Wan or the Internet.
c] Setup SAN - Storage array.
d] To setup loadbalanced webcluser using cluster aware Linux file system etc.

In this tutorial you will learn how to have a fully functional Linux iSCSI SAN using tgt framework.]]> http://www.cyberciti.biz/tips/howto-setup-linux-iscsi-target-sanwith-tgt.html/feed 26 http://www.cyberciti.biz/tips/start-stop-vmware-virtualization-vms-command.html http://www.cyberciti.biz/tips/start-stop-vmware-virtualization-vms-command.html#comments Wed, 29 Oct 2008 07:02:41 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3235 You can easily start / stop / pause or take a snapshot from a shell prompt under a Linux / Windows host using vmrun command. This is useful if you do not want to run web interface for starting and/or stopping VMs.]]> http://www.cyberciti.biz/tips/start-stop-vmware-virtualization-vms-command.html/feed 5 http://www.cyberciti.biz/tips/raid5-vs-raid-10-safety-performance.html http://www.cyberciti.biz/tips/raid5-vs-raid-10-safety-performance.html#comments Wed, 22 Oct 2008 12:48:43 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3155 A Redundant Array of Independent Drives (or Disks), also known as Redundant Array of Inexpensive Drives (or Disks) (RAID) is an term for data storage schemes that divide and/or replicate data among multiple hard drives. RAID can be designed to provide increased data reliability or increased I/O performance, though one goal may compromise the other. There are 10 RAID level. But which one is recommended for data safety and performance considering that hard drives are commodity priced? ]]> http://www.cyberciti.biz/tips/raid5-vs-raid-10-safety-performance.html/feed 71 http://www.cyberciti.biz/tips/seagates-barracuda-15tb-hard-disk.html http://www.cyberciti.biz/tips/seagates-barracuda-15tb-hard-disk.html#comments Tue, 21 Oct 2008 18:53:46 +0000 nixCraft http://www.cyberciti.biz/tips/?p=3149 Wow, this is a large size desktop hard disk for storing movies, tv shows, music / mp3s, and photos. You can also load multiple operating systems using vmware or other software for testing purpose. This hard disk comes with 5 year warranty and can transfer at 300MB/s. But, How reliable is the 1.5TB hard disk?]]> http://www.cyberciti.biz/tips/seagates-barracuda-15tb-hard-disk.html/feed 1 http://www.cyberciti.biz/tips/centos-rhel-poor-nfs-write-performance.html http://www.cyberciti.biz/tips/centos-rhel-poor-nfs-write-performance.html#comments Fri, 22 Aug 2008 09:41:58 +0000 nixCraft http://www.cyberciti.biz/tips/?p=2759 A few days ago I noticed that NFS performance between a web server node and NFS server went down by 50%. NFS was optimized and the only thing was updated Red Hat kernel v5.2. I also noticed same trend on CentOS 5.2 64 bit edition.]]> http://www.cyberciti.biz/tips/centos-rhel-poor-nfs-write-performance.html/feed 4 http://www.cyberciti.biz/tips/linux-filesystem-benchmarking-with-iozone.html http://www.cyberciti.biz/tips/linux-filesystem-benchmarking-with-iozone.html#comments Fri, 04 Jul 2008 09:15:40 +0000 nixCraft http://www.cyberciti.biz/tips/?p=2437 http://www.cyberciti.biz/tips/linux-filesystem-benchmarking-with-iozone.html/feed 7