Tech Trace

Running "strace" on my day

[techtrace-blog]

Increasing a Linux Logical volume and file system

LVM is a logical Volume manager for the Liner Kernel; it manages disk drives and similar mass-storage devices.

A number of tools are provided for configuring LVM volumes and volume groups on most linux distributions. The first step is to gather information on file-system that we want to increase.

Use df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/vg_talhafedoravbox-lv_root

                           76G   16G   60G  21% /

tmpfs                  625M  8.2M  616M   2% /dev/shm

/dev/sda1             485M   49M  411M  11% /boot

Now lets say we want to increase the root filesystem on Volume Group vg_talhafedorabox. Then we need to figure out whether we have enough space available in that volume group.

Use

vgdisplay

 --- Volume group ---

  VG Name               vg_talhafedoravbox

  System ID             

  Format                lvm2

  Metadata Areas        2

  Metadata Sequence No  7

  VG Access             read/write

  VG Status             resizable

  MAX LV                0

  Cur LV                2

  Open LV               2

  Max PV                0

  Cur PV                2

  Act PV                2

  VG Size               79.47 GiB

  PE Size               32.00 MiB

  Total PE              2543

  Alloc PE / Size       2528 / 79.00 GiB

  Free  PE / Size       15 / 480.00 MiB

  VG UUID               SfbvVi-9mbU-c9zH-qNlO-mKpu-dY95-kqMEr0

The "Free PE/Size" shows the free space available to us in this volume group

Now to resize the vg,

Use

lvresize -L +480M /dev/mapper/vg_talhafedoravbox-lv_root

This command adjusts the size of the specified logical volume. Keep in mind, however, that this change is much like a change to a partition alone. That is, the size of the file system contained in the logical volume is not altered. To adjust the file system, you must use a file system-specific tool, such as resize2fs, resizereiserfs, xfs_growfs, or the resize mount option when mounting Journaled File System (JFS).

For ext2/ext3/ext3 systems Use

resize2fs -p  /dev/mapper/vg_talhafedoravbox-lv_root

You can now check with df -h to confirm the new file-system size

[techtrace-blog]

VXLAN: The new approach to virtual L2 networks

VXLAN is an enhancement over the traditional VLAN technology. VLANs have been around for some time now. VXLANs address some of the key issues faced by VLANs.

1. A limit of only 4096 network segments is imposed due to the VLAN ID field. This limits the scope in large data-centers.

2. VLAN and its switching boundaries are not flexible nor easily extensible.

3. Operational inefficient fault tolerance.

VXLANs provide a method for so called "floating" virtual domains on top of a common networking and virtualization infrastructure. Using VXLANs a large number of virtual domains can be created above an existing network with complete isolation from each other and underlying network.

VXLANs work by creating Layer 2 logical networks on top of standard Layer 3 networks. This means that Layer 2 frames are encapsulated in Layer 3 IP packets. A "Segment ID" in every frame differentiates the VXLAN logical networks from each other without any need for VLAN tags. This allows very large numbers of isolated L2 VXLAN networks to co-exist on a common L3 infra.

VXLANs operate using encapsulation unlike VLANs which insert a 802.1Q header between the MAC and IP header of the original packet. This means that VXLANs offer a new form of tunnel encapsulation as well.

Exact protocol level headers and further info available here:

http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-02

[techtrace-blog]

The interactive Linux kernel map helps you traverse complex interconnections between subsystems of the kernel while you explore its source code. A Linux hacker, trying to track down a bug or just understand how some subsystem works, can get exhausted just trying to figure out what invokes what — so the kernel map comes to the rescue!

The map depicts over 400 prominent functions and structures divided into major subsystems. You can zoom in on any function and move about the functions graphically. The relationships among all functions are shown through connecting lines, and clicking on any function takes you to source code in the Linux Cross Reference and the collection of Linux kernel documentation.

[techtrace-blog]

Linux Kernel: Networking(Part-1)

Lets try to understand the basics of networking system in the Linux kernel. It requires a lot of effort to gather the bits from all over the places like magazine posts, email thread, articles to source code to get a handle on the various parts of the networking system in the Linux kernel. While at it, i thought of arranging the material in a consise series of posts, both for my own reference and other to read up on....So lets start