Networking at home

We all know that to have the array device names persist you have to do:  mdadm --detail --scan >>/etc/mdadm/mdadm.conf However this is not enough, this has to be also updated in initram, so the easiest way to do it, is by running: dpkg-reconfigure mdadm This will automatically update the initram. (I do not mention here, that after piping the array list to /etc/mdadm/mdadm.conf, it is very practical to manually check if everything is correct, to avoid duplicate arrays or old not-any-more existing arrays.)

I have experienced very poor performance on the RAID set up on my new computer, so I decided to do a short test of the speed and capacity of different RAID configurations.

Deduplication means, that when saving data to disks, if the same data is stored once more, then only a reference is stored and space is saved. OpenDedup is an open source online (real-time) deduplication solution, with one of the goals to provide a solution for storing Virtual Machine images, where big parts of the images could be duplicated. In this article we test OpenDedup, both from speed and compression point of view.

This is a test performed on an Ubuntu 1604 virtual machine, to verify, how you can expand a SW RAID, which is used trough an LVM by a file system, without losing data.

Now I am setting up a new NAS and to be able to decide if I should use Stripped LVM I did some measurements. Stripped LVM means the the data volume is spread across 2 physical disks and data reads and writes are executed in parallel to the two disks, so in theory this will duplicate the disks speed. However stripping has one disadvantage that if one of the disks fails then all data is lost, while with normal volumes, there are chances that from the functional disk it is possible to restore the data. The NAS has a Gigabit Ethernet LAN connection so in theory 125 MBytes/sec speeds can be achieved. To do the tests I have set up two 200 GByte logical volumes on the LVM containing two 4 Tbytes physical disks, one stripped across the two disks and the other without stripping. First I measured the speed within the NAS, using the linux DD command: On the normal volume: >dd if=/dev/zero of=/media/data/Adatok/test bs=1M count=2000      2000+0 records in 2000+0 records out...