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What is Greyhole

Greyhole is Amahi's Storage pooling technology. Storage Pooling combines the space of multiple disk drives and makes them look as if they were all part of a single pool of disk space. Specifically, Greyhole:

  • Combines the space from multiple drives into a single volume
  • Distributes files across all drives in the pool
  • Creates multiple copies of files in admin-specified shares


You can add additional drives to your hda and prepare them for use in Greyhole by following using the Amahi Disk Wizard application for Amahi 7. All others use adding a second hard drive to your HDA guidance.

Warning!
You should NEVER change or delete files in the shared directories (/var/hda/files/* by default) directly on the HDA, using the terminal, or the Gnome file browser, for the shares for which you checked the Uses pool option in the Amahi dashboard. If you want to work with files on Greyhole shares on the HDA, you should Mount Shares Locally.


You should be safe reading existing files directly, or adding new files directly, as long as don't care that your new files will only be moved into the storage pool during the next check, which runs automatically at midnight (or manually using greyhole --fsck). Until then, your new files will be stored in your shared directories (normally /var/hda/files/share_name/).

Also, touching anything inside the gh directories that Greyhole creates at the root of your partitions is a recipe for disaster. We strongly discourage you from using the root partition in a drive pool.


NOTE: All commands are executed as root user (Fedora) or preceded with sudo (Ubuntu).

Amahi 7

Amahi application Greyhole UI provides this capability. Refer to the Greyhole UI Application Transition guide for details on installation and configuration.

NOTE: If you would still like to setup your Greyhole pool manually, please see Manual Greyhole Setup.

Amahi 6

You need to go in the Settings tab, and select Enable Advanced Settings. Without Advanced Settings enabled, you won't see the following page and options.

Storage Pool

Storage Pool 1.png

Select the drives you want available for your storage pool.

Share Options

The next step is to select the share you want to replicate across the pool.

From the Shares tab, select the Shares sub-catagory. We chose the Pictures share for this tutorial.

Greyhole Options 1.png

Check the option for "Uses pool" and choose the number of drives to replicate this share. In this instance we have chosen to use all drives available to the greyhole pool.

NOTE: Greyhole is not a backup solution. If a file is removed, all copies are removed.

Advanced Options

You can further configure Greyhole by manually editing /var/hda/platform/html/config/greyhole.yml.

NOTE: Options duplicated in /etc/greyhole.conf will be overridden by grehole.yml.

To see what options are available, and what they do, refer to the sample greyhole.conf provided with Greyhole.

greyhole.yml is in in YAML format. Most of it should be easy enough to modify. The only exception would be the sticky_files (and optional sticky_into) options.

Here's an example of how those should appear:

To specify the following to Greyhole in greyhole.conf:

sticky_files = Music/
 sticky_files = Videos/Movies/
     stick_into = /mnt/hdd1/gh
     stick_into = /mnt/hdd5/gh
 sticky_files = Backups/CrashPlan/
     stick_into = /mnt/hdd0/gh

one should specify this in the greyhole.yml file, where precise indentation matters:

sticky_files: 
 - - Music/
 - - Videos/Movies/
   - - /mnt/hdd1/gh
     - /mnt/hdd5/gh
 - - Backups/CrashPlan/
   - - /mnt/hdd0/gh

Once finished, it's important that you check to see the file is properly formatted. To do so, do the following:

cd /var/hda/platform/html/config
echo 'require "yaml"; YAML::load(File.open("greyhole.yml"))' | irb

If you do not see any errors, then your ready for the next step. Otherwise, ensure you correct the errors before proceeding.

For the changes to be effective, you will need to force Amahi to:

Ubuntu
Regenerate the greyhole.conf file by editing a share, clicking it's path, and just clicking the Save button without actually changing the path.
Fedora
Restart the Dashboard with any one of these alternatives as root user:
  • touch /var/hda/platform/html/tmp/restart.txt
  • systemctl restart httpd.service
  • reboot
Then regenerate the greyhole set up by changing any setting in Shares or in Drive pooling.

Tips and Best Practices

Refer to Greyhole Tips for additional guidance.

Testing and Reliability

Check out the Greyhole grinder to help make Greyhole rock solid.

References

  • Good article on Greyhole with terms explained.