Cache Configuration

Nodeum Disk Caching introduction

Nodeum uses this Disk Caching mechanism to define the virtual file system which are used in conjunction with the Container. This will allow a Global Virtualization of your different secondary storage and provide file system representation. This is also named as an active archive solution.

The prerequisite is to have an available disk caching system with is seen as a /dev/ device or a mounted device. Some supported disk caching systems:

Internal RAID on local disks
Internal RAID on JBOD
SCSI Attached Storage
Linux-based block replication (e.g. DRBD, ...)
Linux-based Cluster (e.g. GlusterFS, …)

How to Enable and Configure a Cache into Nodeum

In the menu settings/hardware/cache, you will see the information related to the current cache system configured.

In this example, there is no cache configured:

How to configure the cache?

First, you have to access your Nodeum server with a console terminal in root and run this script /opt/nodeum/bin/core/cache_disk_format.sh /dev/sdx (replace sdx by the correct device, likely sdb). This script will create the CACHE Disk.

There is a second step which the CACHE Disk selection and configuration. You can execute this second script: /opt/nodeum/bin/core/cache_disk_select.sh /dev/sdx (where sdx is the same device as the previous step). Then the process will start.

The initialization can take some minutes depending the size of the disk.

Once initialized, in the Nodeum WebGUI, you can verify that the CACHE Disk is configured as a cache for Nodeum. You will see Ready and Used as Cacheyou will that your cache is well configured.

Advanced Settings

iSCSI Storage as Cache

In this case, the Linux automount can execute a disk mounting in a different order that the one you will expect. This means that if, for example, the disk "cache" you plan to use is defined in a network-attached volume or an iscsi target, by nature, the network has to be enabled before trying to mount the "cache" disk.

The fstab configuration of a standard cache is defined in the file /etc/fstab, here are the default settings.

...
/dev/sdb1   /mnt/CACHE   ext4   rw,user_xattr   0   0
...

In this definition, a dependency on the network is missing and have to be added.

There are different way to define this dependencies:

Directly in the fstab

Another option, it is also possible to add _netdev directly in the fstab , the setting _netdev :

...
/dev/sdb1   /mnt/CACHE   ext4   rw,user_xattr,_netdev   0   0
...

In changing the automount service

In this case, the mnt-CACHE.mount script needs to be edited to add required dependencies

For this you need to :

Edit the file /run/systemd/generator/mnt-CACHE.mount
Add the "After" - "Required" directives

Here is an example of a file including these directives :

[root@nodeum]# cat /run/systemd/generator/mnt-CACHE.mount
# Automatically generated by systemd-fstab-generator

[Unit]
SourcePath=/etc/fstab
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
Before=local-fs.target

After=iscsi.service 
Requires=iscsi.service

[Mount]
What=/dev/sdb1
Where=/mnt/CACHE
Type=ext4
Options=rw,user_xattr,_netdev

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