113 lines
5.0 KiB
Markdown
113 lines
5.0 KiB
Markdown
|
## Fault Management Logic for ZED ##
|
||
|
|
|
||
|
|
The integration of Fault Management Daemon (FMD) logic from illumos
|
||
|
|
is being deployed in three phases. This logic is encapsulated in
|
||
|
|
several software modules inside ZED.
|
||
|
|
|
||
|
|
### ZED+FM Phase 1 ###
|
||
|
|
|
||
|
|
All the phase 1 work is in current Master branch. Phase I work includes:
|
||
|
|
|
||
|
|
* Add new paths to the persistent VDEV label for device matching.
|
||
|
|
* Add a disk monitor for generating _disk-add_ and _disk-change_ events.
|
||
|
|
* Add support for automated VDEV auto-online, auto-replace and auto-expand.
|
||
|
|
* Expand the statechange event to include all VDEV state transitions.
|
||
|
|
|
||
|
|
### ZED+FM Phase 2 (WIP) ###
|
||
|
|
|
||
|
|
The phase 2 work primarily entails the _Diagnosis Engine_ and the
|
||
|
|
_Retire Agent_ modules. It also includes infrastructure to support a
|
||
|
|
crude FMD environment to host these modules. For additional
|
||
|
|
information see the **FMD Components in ZED** and **Implementation
|
||
|
|
Notes** sections below.
|
||
|
|
|
||
|
|
### ZED+FM Phase 3 ###
|
||
|
|
|
||
|
|
Future work will add additional functionality and will likely include:
|
||
|
|
|
||
|
|
* Add FMD module garbage collection (periodically call `fmd_module_gc()`).
|
||
|
|
* Add real module property retrieval (currently hard-coded in accessors).
|
||
|
|
* Additional diagnosis telemetry (like latency outliers and SMART data).
|
||
|
|
* Export FMD module statistics.
|
||
|
|
* Zedlet parallel execution and resiliency (add watchdog).
|
||
|
|
|
||
|
|
### ZFS Fault Management Overview ###
|
||
|
|
|
||
|
|
The primary purpose with ZFS fault management is automated diagnosis
|
||
|
|
and isolation of VDEV faults. A fault is something we can associate
|
||
|
|
with an impact (e.g. loss of data redundancy) and a corrective action
|
||
|
|
(e.g. offline or replace a disk). A typical ZFS fault management stack
|
||
|
|
is comprised of _error detectors_ (e.g. `zfs_ereport_post()`), a _disk
|
||
|
|
monitor_, a _diagnosis engine_ and _response agents_.
|
||
|
|
|
||
|
|
After detecting a software error, the ZFS kernel module sends error
|
||
|
|
events to the ZED user daemon which in turn routes the events to its
|
||
|
|
internal FMA modules based on their event subscriptions. Likewise, if
|
||
|
|
a disk is added or changed in the system, the disk monitor sends disk
|
||
|
|
events which are consumed by a response agent.
|
||
|
|
|
||
|
|
### FMD Components in ZED ###
|
||
|
|
|
||
|
|
There are three FMD modules (aka agents) that are now built into ZED.
|
||
|
|
|
||
|
|
1. A _Diagnosis Engine_ module (`agents/zfs_diagnosis.c`)
|
||
|
|
2. A _Retire Agent_ module (`agents/zfs_retire.c`)
|
||
|
|
3. A _Disk Add Agent_ module (`agents/zfs_mod.c`)
|
||
|
|
|
||
|
|
To begin with, a **Diagnosis Engine** consumes per-vdev I/O and checksum
|
||
|
|
ereports and feeds them into a Soft Error Rate Discrimination (SERD)
|
||
|
|
algorithm which will generate a corresponding fault diagnosis when the
|
||
|
|
tracked VDEV encounters **N** events in a given **T** time window. The
|
||
|
|
initial N and T values for the SERD algorithm are estimates inherited
|
||
|
|
from illumos (10 errors in 10 minutes).
|
||
|
|
|
||
|
|
In turn, a **Retire Agent** responds to diagnosed faults by isolating
|
||
|
|
the faulty VDEV. It will notify the ZFS kernel module of the new VDEV
|
||
|
|
state (degraded or faulted). The retire agent is also responsible for
|
||
|
|
managing hot spares across all pools. When it encounters a device fault
|
||
|
|
or a device removal it will replace the device with an appropriate
|
||
|
|
spare if available.
|
||
|
|
|
||
|
|
Finally, a **Disk Add Agent** responds to events from a libudev disk
|
||
|
|
monitor (`EC_DEV_ADD` or `EC_DEV_STATUS`) and will online, replace or
|
||
|
|
expand the associated VDEV. This agent is also known as the `zfs_mod`
|
||
|
|
or Sysevent Loadable Module (SLM) on the illumos platform. The added
|
||
|
|
disk is matched to a specific VDEV using its device id, physical path
|
||
|
|
or VDEV GUID.
|
||
|
|
|
||
|
|
Note that the _auto-replace_ feature (aka hot plug) is opt-in and you
|
||
|
|
must set the pool's `autoreplace` property to enable it. The new disk
|
||
|
|
will be matched to the corresponding leaf VDEV by physical location
|
||
|
|
and labeled with a GPT partition before replacing the original VDEV
|
||
|
|
in the pool.
|
||
|
|
|
||
|
|
### Implementation Notes ###
|
||
|
|
|
||
|
|
* The FMD module API required for logic modules is emulated and implemented
|
||
|
|
in the `fmd_api.c` and `fmd_serd.c` source files. This support includes
|
||
|
|
module registration, memory allocation, module property accessors, basic
|
||
|
|
case management, one-shot timers and SERD engines.
|
||
|
|
For detailed information on the FMD module API, see the document --
|
||
|
|
_"Fault Management Daemon Programmer's Reference Manual"_.
|
||
|
|
|
||
|
|
* The event subscriptions for the modules (located in a module specific
|
||
|
|
configuration file on illumos) are currently hard-coded into the ZED
|
||
|
|
`zfs_agent_dispatch()` function.
|
||
|
|
|
||
|
|
* The FMD modules are called one at a time from a single thread that
|
||
|
|
consumes events queued to the modules. These events are sourced from
|
||
|
|
the normal ZED events and also include events posted from the diagnosis
|
||
|
|
engine and the libudev disk event monitor.
|
||
|
|
|
||
|
|
* The FMD code modules have minimal changes and were intentionally left
|
||
|
|
as similar as possible to their upstream source files.
|
||
|
|
|
||
|
|
* The sysevent namespace in ZED differs from illumos. For example:
|
||
|
|
* illumos uses `"resource.sysevent.EC_zfs.ESC_ZFS_vdev_remove"`
|
||
|
|
* Linux uses `"sysevent.fs.zfs.vdev_remove"`
|
||
|
|
|
||
|
|
* The FMD Modules port was produced by Intel Federal, LLC under award
|
||
|
|
number B609815 between the U.S. Department of Energy (DOE) and Intel
|
||
|
|
Federal, LLC.
|
||
|
|
|