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Simple Method to Benchmark Disk Read & Write Speeds From the Linux Command Line

Recently, I’ve been exploring high availability iSCSI targets and using them as virtual machine storage. I have always been a bit weary of iSCSI performance over gigabit networks due to some not-so-great experiences many years ago. iSCSI technology has progressed quite a bit since then. FreeNAS has an excellent implementation of iSCSI, as well as Nexenta. I wanted to get a good grasp on how well everything was performing, so I decided to run some basic benchmarks.

The virtual machine I’m working with has Ubuntu 15.04 installed, but these commands will work on just about any linux distribution in existence. The hyperviser is running VMware ESXi 6, with this particular virtual machine stored on an iSCSI target served from a FreeNAS virtual machine running on another VMware ESXi hyperviser. The FreeNAS virtual machine has been given PCI Passthrough to a 3ware 9650SE-16ML, connected to 4x1TB Hitachi SATA Hard Drives exported as JBOD (individual drives, no RAID). FreeNAS configured a RAID10 with the four drives, which is where the iSCSI target resides. The network is gigabit, with an Adtran NetVanta 1524ST switch. I have not enabled Jumbo Frames. The theoretical maximum transfer speed on a gigabit network is about 125MB/s. Of course, with the overhead associated with TCP/IP and iSCSI encapsulation, a single link should be a little less. Lets get started.

To test WRITE speed of hard disk using the DD command:

#  sync; dd if=/dev/zero of=tempfile bs=1M count=1024; sync
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 10.8496 s, 99.0 MB/s

So, this command writes a bunch of zeros to a file called tempfile, with a size of 1024MB. If you want to use a larger test file, you can change “1024” to a higher number. For instance, changing 1024 to 10000 would write a 10GB temp file. This command only tests the write speed. As you can see, the reported write speed was 99MB/s, not too shabby.

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Expanding & Resizing an LVS Partition / Group on Ubuntu 14.04 LTS

I have a server dedicated to the purpose of hosting an ownCloud instance. OwnCloud 8 to be exact. It’s an Ubuntu 14.04 LTS virtual machine, on an ESXi 5 hypervisor. This is my own server, and not any sort of revenue generating customer service. It has become a “Dropbox” replacement for myself, and a few select friends and family. Recently, I found the original 1TB I allocated to be filling up quickly. So, I started doing some google searches to see how I could go about resizing, or expanding, an LVM group (like a partition). I found an enormous wealth of information, much of it conflicting. As I started going through a guide, that closely matched my configuration (everything was the same, actually, except the size of the disk), I instantly faced problems with commands not working. It was frustrating. Eventually I navigated through it and successfully expanded the Logical Volume. I figured I would go ahead and document my troubles so that I can make others lives a little easier.

Firstly, you need to run a couple commands to see what you’re working with. These commands are df and fdisk -l. You should see something like this:

mike@cloud:~$ df
Filesystem                  1K-blocks     Used Available Use% Mounted on
/dev/mapper/cloud--vg-root 1048254140 65112056 929870740   7% /
none                                4        0         4   0% /sys/fs/cgroup
udev                          4077252        4   4077248   1% /dev
tmpfs                          817700      524    817176   1% /run
none                             5120        0      5120   0% /run/lock
none                          4088496        0   4088496   0% /run/shm
none                           102400        0    102400   0% /run/user
/dev/sda1                      240972    67164    161367  30% /boot


mike@cloud:~$ sudo fdisk -l
[sudo] password for mike:

Disk /dev/sda: 1099.5 GB, 1099511627776 bytes
255 heads, 63 sectors/track, 133674 cylinders, total 2147483648 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 identifier: 0x000c9595

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      499711      248832   83  Linux
/dev/sda2          501758  2147481599  1073489921    5  Extended
/dev/sda5          501760  2147481599  1073489920   8e  Linux LVM

Disk /dev/mapper/cloud--vg-root: 1090.7 GB, 1090661646336 bytes
255 heads, 63 sectors/track, 132598 cylinders, total 2130198528 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 identifier: 0x00000000

Disk /dev/mapper/cloud--vg-root doesn't contain a valid partition table

Disk /dev/mapper/cloud--vg-swap_1: 8589 MB, 8589934592 bytes
255 heads, 63 sectors/track, 1044 cylinders, total 16777216 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 identifier: 0x00000000

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