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  • Adding a New Disk to a Linux Server and Creating an LVM Partition
    10/20/2017 1:43PM
    There are a number of tutorials online for adding a new disk to a machine and then extending an existing LVM partition to use the new device.

    This particular tutorial covers the use case of adding a new disk to a Linux server and then creating a NEW LVM partition on it without modifying the existing devices and LVM partitions.

    The first thing you will need to do is add the physical device to the server (or VM).

    Then, you need to confirm that the OS can 'see' the device.  The following command will show you the list of avaiable disk devices.

    # fdisk -l

    Disk /dev/sdb: 80.5 GB, 80530636800 bytes, 157286400 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes


    Here, we see that the OS can 'see' the /dev/sdb device.  For the rest of this tutorial, we will assume that your new device is /dev/sdb.

    Using fdisk, create a primary partition on the new device

    # fdisk /dev/sdb
    Welcome to fdisk (util-linux 2.23.2).

    Changes will remain in memory only, until you decide to write them.
    Be careful before using the write command.

    Device does not contain a recognized partition table
    Building a new DOS disklabel with disk identifier 0xc78ce5fd.

    Command (m for help): n
    Partition type:
       p   primary (0 primary, 0 extended, 4 free)
       e   extended
    Select (default p): p
    Partition number (1-4, default 1):
    First sector (2048-157286399, default 2048):
    Using default value 2048
    Last sector, +sectors or +size{K,M,G} (2048-157286399, default 157286399):
    Using default value 157286399
    Partition 1 of type Linux and of size 75 GiB is set

    Command (m for help): w
    The partition table has been altered!

    Calling ioctl() to re-read partition table.
    Syncing disks.


    After partitioning re-run fdisk to list the partitions

    # fdisk -l

    Disk /dev/sdb: 80.5 GB, 80530636800 bytes, 157286400 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk label type: dos
    Disk identifier: 0xc78ce5fd

       Device Boot      Start         End      Blocks   Id  System
    /dev/sdb1            2048   157286399    78642176   83  Linux


    Now, create an LVM Physical Volume (PV)

    # pvcreate /dev/sdb1
      Physical volume "/dev/sdb1" successfully created.


    Create the LVM Volume Group (VG)

    # vgcreate centos_repos /dev/sdb1
      Volume group "centos_repos" successfully created


    Execute the vgdisplay command to list all of the Volume Groups

    # vgdisplay

      --- Volume group ---
      VG Name               centos_repos
      System ID             
      Format                lvm2
      Metadata Areas        1
      Metadata Sequence No  1
      VG Access             read/write
      VG Status             resizable
      MAX LV                0
      Cur LV                0
      Open LV               0
      Max PV                0
      Cur PV                1
      Act PV                1
      VG Size               75.00 GiB
      PE Size               4.00 MiB
      Total PE              19199
      Alloc PE / Size       0 / 0   
      Free  PE / Size       19199 / 75.00 GiB
      VG UUID               FDgd3y-keqV-riq6-vb46-C2F5-JJa2-Ew2DW4


    Create a LVM Logical Volume (LV).  In this case I am going to use the entire drive

    # lvcreate -n repos --size 74.9G centos_repos
      Rounding up size to full physical extent 74.90 GiB
      Logical volume "repos" created.


    lvdisplay will list all of the existing Logical Volumes

    # lvdisplay
    ...
      --- Logical volume ---
      LV Path                /dev/centos_repos/repos
      LV Name                repos
      VG Name                centos_repos
      LV UUID                pvNLX4-3wTf-2eMY-RebF-WnFU-8y9F-BRidMn
      LV Write Access        read/write
      LV Creation host, time nebula, 2017-10-20 17:36:38 +0000
      LV Status              available
      # open                 0
      LV Size                74.90 GiB
      Current LE             19175
      Segments               1
      Allocation             inherit
      Read ahead sectors     auto
      - currently set to     8192
      Block device           253:4


    Now we need to format the LV.  In this case we will use ext4, you may choose another filesystem format.  Be sure to use the LV Path returned by lvdisplay.

    # mkfs.ext4 /dev/centos_repos/repos
    mke2fs 1.42.9 (28-Dec-2013)
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    Stride=0 blocks, Stripe width=0 blocks
    4915200 inodes, 19635200 blocks
    981760 blocks (5.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=2168455168
    600 block groups
    32768 blocks per group, 32768 fragments per group
    8192 inodes per group
    Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000, 7962624, 11239424

    Allocating group tables: done                            
    Writing inode tables: done                            
    Creating journal (32768 blocks): done
    Writing superblocks and filesystem accounting information: done   


    Now you can mount the file system as usual and/or add it to /etc/fstab.

  • How To Benchmark Disk I/O
    08/14/2014 12:24PM

    Here is a quick snipped on how to benchmark Disk I/O with dd.

    $ time sh -c "dd if=/dev/zero of=/home/rchapin/test.zeros bs=1024k count=10000 && sync"

    10000+0 records in
    10000+0 records out
    10485760000 bytes (10 GB) copied, 81.4124 s, 129 MB/s

    real    1m21.950s
    user    0m0.810s
    sys     0m5.474s


    Will do a write test of 10GB.

    You can do a similar test and read from that file generated and write to another file or /dev/null to get an idea of the read speeds.

    See the this link for more information.

  • Clone and Backup a Bootable USB Drive
    03/09/2014 10:19AM

    We recently got a new ASUS laptop for the boys to use (I'll use it too, it's pretty sweet) which came with Windows 8.

    It did not come with the install CD or license key, but included a recovery partition and the key in the BIOS.  Now that we've had it for a few weeks and verified that all of the hardware works, we are going to put Ubuntu on it, but I wanted to make sure that I would still be able to use the Windows 8 license on it if I wanted.

    So, using the Win8 recovery program, I createad a bootable recovery disk onto a USB stick and I wanted to back it up, as well as be able to make a clone of it if need be.

    Following are the dd commands to make that happen:

    First, do a tail of /var/log/messages before you plug in the usb drive.  You should see it be recognized by the machine as sd[something].  Or, you can do an fdisk -l and should see the usb stick (as well as the other drives on your machine)

    Be warned, make sure that you have the devices correct before you run these commands or you may destroy data on your machine.

    Assuming that the usb stick is sdg, clone the disk to a file on another computer

    dd if=/dev/sdg of=./windows_8_rcvry_usb_asus.dd conv=notrunc

    Copy the file to another USB stick (assuming that /dev/sdg is the USB drive because all data on /dev/sdg will be destroyed during this operation):

    dd if=./windows_8_rcvry_usb_asus.dd of=/dev/sdg conv=notrunc

    Just make sure that the usb drive to which you are copying is the same size or larger than the original one that you copied from.

  • Problems with WD Caviar Green SATA Drives
    11/06/2009 1:28PM

    I needed a couple of 1 TB SATA drives to put into external enclosures.

    I have found that in many cases MicroCenter offers prices very close to that found on Amazon, and/or Buy.com.? The thing that I really like about MicroCenter is that they actually have knowledgeable sales people.? When seeing if the drives that I was looking for were in stock the sales associated told me that I wanted to stay away from any of the "Green" drives.? In his experience, not only were they considerably slower (which in this case, didn't make much of a difference to me) but that their reliability was very poor.? The "Green" drives spin at variable speeds so that they will consume less energy.? Evidently, the variable speed mechanism hasn't been sorted out completely and results in catastrophic hardware failure.

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