Configuring HDD Hot Plugging

Maintaining a large cluster (see Recommended Configuration ) with many hosts and multiple HDDs per host requires a simple automated solution to easily add new and replace failed HDDs.

Linux has had support for handling such tasks for a long time. In Linux, each time an HDD is inserted or removed, the kernel generates an event which is passed to the udev device manager that allows the system to process the event further.

pstorage-hotplugd is a set of scripts which use udev and enable you to automatically create and start a CS on an HDD hot plug event and stop a CS on an HDD hot unplug event (stopped chunk servers need to be deleted manually).

Warning: Special considerations apply to sharing SSD write cache between running CSes. This functionality is not implemented yet, so chunk servers with SSD journals will not be started automatically on disk hotplug.

To enable and configure hotplugging, set the parameters in the configuration file as described in Setting Hotplugging Parameters .

Disk Hot Plug Sequence

When you connect an HDD while hotplug is enabled, the following happens:

1. The new HDD is detected. If it does not have a partition table or has an empty partition table, a single partition spanning the entire HDD is created, formatted to ext4, and labelled pstorage-hotplug . Otherwise the HDD is ignored.
2. The partition labelled pstorage-hotplug is detected, mounted to a unique location, and checked for an existing CS on it.

   Note: Such a partition can be created either automatically (see the first step above) or manually as described in Partitioning the Disk Manually .

3. If a CS is found, it is added to the list of CSes on this host and started. Otherwise, a new CS is created for the specified cluster and started.

Disk Hot Unplug Sequence

When you disconnect an HDD while hotplug is enabled, the following happens:

1. The HDD removal is detected.
2. All CSes running on the HDD are automatically stopped, and the HDD is logically unmounted.

   Note: If you unplugged a wrong HDD, plug it back and the CSes on it will automatically restart.

Notes:

1. You cannot manage metadata servers with the pstorage-hotplugd scripts.

2. Hot plugging and unplugging currently works for HDDs connected to LSI RAID controllers. Such HDDs must work in the passthrough mode (JBOD) or RAID0. For the list of supported LSI RAID controllers, see Supported RAID Controllers .