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Samba 4: Linux Active Directory Server

Linux does have directory server called OpenLDAP, but it requires good understanding and admin skills. MS-Ad has reputation for ease of use. Samba is a free software re-implementation of SMB/CIFS networking protocol mainly used by Microsoft. One of the goals of Samba version 4 is to implement an Active Directory compatible Domain Controller. Major features for Samba 4 already include:
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Get ready for a minute with 61 seconds. Scientists are delaying the start of 2009 by the first 'leap second' a timing tweak meant to make up for changes in the Earth's rotation.

The aged Earth is slowing down in its daily rotation, at least in the current epoch. So a leap second is added (a one-second adjustment added) to our time. This year will be exactly one second longer.

Precise time measurements are needed for high-speed communications systems among other modern technologies such as clusters, GPS, networks. You need to make sure that you are running updated version of ntpd that support leap second for UNIX and Windows computers.
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Top 10 Linux Virtualization Software

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.
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Download of the day: WordPress 2.7

WordPress version 2.7 has been released and available for download. From the announcement page:

The first thing you'll notice about 2.7 is its new interface. From the top down, we've listened to your feedback and thought deeply about the design and the result is a WordPress that’s just plain faster. Nearly every task you do on your blog will take fewer clicks and be faster in 2.7 than it did in a previous version.

What is new in WordPress 2.7

For a visual introduction to what 2.7 is, check out this video (available in HD, and full screen):

Download the latest release of WordPress version 2.7, released on 10 December 2008 (via official blog).

Every IT shop has a mix of Windows and Linux system. Sometime you need to authenticate your Linux desktop system against Microsoft Active Directory service. You can save time, effort and IT infrastructure by sharing authentication server. This article explains how to setup the Linux desktop computers with Active Directory using Samba and winbind.

From the article:
Starting with Windows 2000, Microsoft moved from NTLM to Active Directory and its integrated Kerberos authentication services. Kerberos was considerably more secure than NTLM, and it scaled better, too. And Kerberos was an industry standard already used by Linux and UNIX systems, which opened the door to integrating those platforms with Windows.

Most Linux distributions come with several PAM authentication modules, including modules that support authentication to an LDAP directory and authentication using Kerberos. You can use these modules to authenticate to Active Directory, but there are some significant limitations, as I will discuss later in this article.

=> Authenticate Linux Clients with Active Directory

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.

vmrun commands

vmrun -u USER -h 'https://vmware.server.com:8333/sdk' -p PASSWORD COMMAND [PARAMETERS]
vmrun -u USER -h 'https://vmware.server.com:8333/sdk' -p PASSWORD start "[storage] Path/to/.vmx"

=> -u USER : VMWare server username

=> -h 'https://vmware.server.com:8333/sdk' : Local or remote server FQDN / IP address

=> -p PASSWORD : VMWare server password

=> COMMAND [PARAMETERS] : Command can be any one of the following:

--------------           ----------           -----------
start                    Path to vmx file     Start a VM
stop                     Path to vmx file     Stop a VM
reset                    Path to vmx file     Reset a VM
suspend                  Path to vmx file     Suspend a VM
pause                    Path to vmx file     Pause a VM
unpause                  Path to vmx file     Unpause a VM

Start a VM called CentOS

To start a virtual machine with Vmware server 2.0 on a Linux host, stored on storage called iscsi:
vmrun -T server -h 'https://vms.nixcraft.in:8333/sdk' -u root -p 'secrete' start "[iSCSI] CentOS52_64/CentOS52_64.vmx"
To start a virtual machine with Workstation on a Windows host (open command prompt by visiting Start > Run > cmd > [enter] key):
vmrun -T ws start "c:\My VMs\centos\centos.vmx"

Stop a VM called CentOS

To stop a virtual machine with Vmware server 2.0 on a Linux host, stored on storage called iscsi:
vmrun -T server -h 'https://vms.nixcraft.in:8333/sdk' -u root -p 'secrete' stop "[iSCSI] CentOS52_64/CentOS52_64.vmx"

Reset a VM called Debian

To reset a virtual machine with Vmware server 2.0 on a Linux host, stored on storage called DISK3:
vmrun -T server -h 'https://sun4k.nixcraft.co.in:8333/sdk' -u root -p 'secrete' reset "[DISK3] Debian5/Debian5.vmx"

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?

I did some research in last few months and based upon my experince I started to use RAID10 for both Vmware / XEN Virtualization and database servers. A few MS-Exchange and Oracle admins also recommended RAID 10 for both safety and performance over RAID 5.

Quick RAID 10 overview (raid 10 explained)

RAID 10 = Combining features of RAID 0 + RAID 1. It provides optimization for fault tolerance.

RAID 0 helps to increase performance by striping volume data across multiple disk drives.

RAID 1 provides disk mirroring which duplicates your data.

In some cases, RAID 10 offers faster data reads and writes than RAID 5 because it does not need to manage parity.

Fig.01: Raid 10 in action

Fig.01: Raid 10 in action

RAID 5 vs RAID 10

From Art S. Kagel research findings:

If a drive costs $1000US (and most are far less expensive than that) then switching from a 4 pair RAID10 array to a 5 drive RAID5 array will save 3 drives or $3000US. What is the cost of overtime, wear and tear on the technicians, DBAs, managers, and customers of even a recovery scare? What is the cost of reduced performance and possibly reduced customer satisfaction? Finally what is the cost of lost business if data is unrecoverable? I maintain that the drives are FAR cheaper! Hence my mantra:

Is RAID 5 Really a Bargain?

Cary Millsap, manager of Hotsos LLC and the editor of Hotsos Journal found the following facts - Is RAID 5 Really a Bargain?":

  • RAID 5 costs more for write-intensive applications than RAID 1.
  • RAID 5 is less outage resilient than RAID 1.
  • RAID 5 suffers massive performance degradation during partial outage.
  • RAID 5 is less architecturally flexible than RAID 1.
  • Correcting RAID 5 performance problems can be very expensive.

My practical experience with RAID arrays configuration

To make picture clear, I'm putting RAID 10 vs RAID 5 configuration for high-load database, Vmware / Xen servers, mail servers, MS - Exchange mail server etc:

RAID LevelTotal array capacityFault toleranceRead speedWrite speed
500GB x 4 disks
1000 GB1 disk4X2X
500GB x 3 disks
1000 GB1 disk2XSpeed of a RAID 5 depends upon the controller implementation

You can clearly see RAID 10 outperforms RAID 5 at fraction of cost in terms of read and write operations.

A note about backup

Any RAID level will not protect you from multiple disk failures. While one disk is off line for any reason, your disk array is not fully redundant. Therefore, old good tape backups are always recommended.

Please add your thoughts and experience in the comments below.

Further readings: