Download of the day: Vmware 2.0 Virtualization Solutions Beta Software

Posted on in Categories CentOS, Download of the day, Hardware, High performance computing, Linux, Linux Virtualization, Networking, vmware last updated October 29, 2008

VMware Server is an entry-level server virtualization solution, which is proprietary, freeware software. VMware released version 2.0 beta of Server on July 1, 2008. New version provides appliance like control using nothing but a webbrowser.

Red Hat / CentOS Linux 4: Setup Device Mapper Multipathing

Posted on in Categories CentOS, data center, fedora linux, File system, Hardware, High performance computing, Howto, kernel, Linux, Linux Scalability, Linux Virtualization, Networking, RedHat/Fedora Linux, Tips last updated December 3, 2008

Multipath I/O is a fault-tolerance and performance enhancement technique whereby there is more than one physical path between the CPU in a computer system and its mass storage devices through the buses, controllers, switches, and bridge devices connecting them.

A simple example would be a SCSI disk connected to two SCSI controllers on the same computer or a disk connected to two Fibre Channel ports. Should one controller, port or switch fail, the operating system can route I/O through the remaining controller transparently to the application, with no changes visible to the applications, other than perhaps incremental latency.

This is useful for:

  1. Dynamic load balancing
  2. Traffic shaping
  3. Automatic path management
  4. Dynamic reconfiguration

Linux device-mapper

In the Linux kernel, the device-mapper serves as a generic framework to map one block device onto another. It forms the foundation of LVM2 and EVMS, software RAIDs, dm-crypt disk encryption, and offers additional features such as file-system snapshots.

Device-mapper works by processing data passed in from a virtual block device, that it itself provides, and then passing the resultant data on to another block device.

How do I setup device-mapper multipathing in CentOS / RHEL 4 update 2 or above?

Open /etc/multipath.conf file, enter:
# vi /etc/multipath.conf
Make sure following line exists and commented out:

devnode_blacklist {
        devnode "*"
}

Make sure default_path_grouping_policy option in the defaults section set to failover. Here is my sample config:

defaults {
       multipath_tool  "/sbin/multipath -v0"
       udev_dir        /dev
       polling_interval 10
       default_selector        "round-robin 0"
       default_path_grouping_policy    failover
       default_getuid_callout  "/sbin/scsi_id -g -u -s /block/%n"
       default_prio_callout    "/bin/true"
       default_features        "0"
       rr_min_io              100
       failback                immediate
}

Save and close the file. Type the following command to load drivers:
# modprobe dm-multipath
# modprobe dm-round-robin

Start the service, enter:
# /etc/init.dmultipathd start
multipath is used to detect multiple paths to devices for fail-over or performance reasons and coalesces them:
# multipath -v2
Turn on service:
# /sbin/chkconfig multipathd on
Finally, create device maps from partition tables:
# kpartx -a /dev/mapper/mpath#
You need to use fdisk on the underlying disks such as /dev/sdc.

References:

  • man page kpartx,multipath, udev, dmsetup and hotplug

How To Measure Linux Filesystem I/O Performance With iozone

Posted on in Categories File system, High performance computing, Linux, Linux distribution, RedHat/Fedora Linux, Storage, Sys admin, Tips, UNIX last updated November 25, 2012

IOzone is a filesystem benchmark tool. The benchmark generates and measures a variety of file operations. Iozone has been ported to many systems and runs under many operating systems including Windows, UNIX, Linux and BSD. This article gives you a jumpstart on performing benchmark on filesystem using iozone a free Filesystem Benchmark utility under Linux.