Announcing GlusterFS release 3.10

[Shyam]

The Gluster community is pleased to announce the release of Gluster 3.10 
(packages available at [1]).

This is a major Gluster release that includes some substantial changes. 
The features revolve around, better support in container environments, 
scaling to larger number of bricks per node, and a few usability and 
performance improvements, among other bug fixes. This releases marks the 
completion of maintenance releases for Gluster 3.7 and 3.9. Moving 
forward, Gluster versions 3.10 and 3.8 are actively maintained.

The most notable features and changes are documented here as well as in 
our full release notes on Github. A full list of bugs that has been 
addressed is included on that page as well.

Major changes and features:

*Brick multiplexing*

Multiplexing reduces both port and memory usage. It does not improve 
performance vs. non-multiplexing except when memory is the limiting 
factor, though there are other related changes that improve performance 
overall (e.g. compared to 3.9).

Multiplexing is off by default. It can be enabled with

# gluster volume set all cluster.brick-multiplex on

*Support to display op-version information from clients*

To get information on what op-version are supported by the clients, 
users can invoke the gluster volume status command for clients. Along 
with information on hostname, port, bytes read, bytes written and number 
of clients connected per brick, we now also get the op-version on which 
the respective clients operate. Following is the example usage:
# gluster volume status <VOLNAME|all> clients

*Support to get maximum op-version in a heterogeneous cluster*

A heterogeneous cluster operates on a common op-version that can be 
supported across all the nodes in the trusted storage pool. Upon upgrade 
of the nodes in the cluster, the cluster might support a higher 
op-version. Users can retrieve the maximum op-version to which the 
cluster could be bumped up to by invoking the gluster volume getcommand 
on the newly introduced global option, cluster.max-op-version. The usage 
is as follows:
# gluster volume get all cluster.max-op-version

*Support for rebalance time to completion estimation*

Users can now see approximately how much time the rebalance operation 
will take to complete across all nodes.

The estimated time left for rebalance to complete is displayed as part 
of the rebalance status. Use the command:
# gluster volume rebalance <VOLNAME> status

*Separation of tier as its own service*

This change is to move the management of the tier daemon into the 
gluster service framework, thereby improving it stability and 
manageability by the service framework.

This has no change to any of the tier commands or user facing interfaces 
and operations.

*Statedump support for gfapi based applications*

gfapi based applications now can dump state information for better 
trouble shooting of issues. A statedump can be triggered in two ways:
a) by executing the following on one of the Gluster servers,
# gluster volume statedump <VOLNAME> client <HOST>:<PID>
     <VOLNAME> should be replaced by the name of the volume
     <HOST> should be replaced by the hostname of the system running the 
gfapi application
     <PID> should be replaced by the PID of the gfapi application

b) through calling glfs_sysrq(<FS>, GLFS_SYSRQ_STATEDUMP) within the 
application
     <FS> should be replaced by a pointer to a glfs_t structure

All statedumps (*.dump.* files) will be located at the usual location, 
on most distributions this would be /var/run/gluster/.

*Disabled creation of trash directory by default*

 From now onwards trash directory, namely .trashcan, will not be be 
created by default upon creation of new volumes unless and until the 
feature is turned ON and the restrictions on the same will be applicable 
as long as features.trash is set for a particular volume.

*Implemented parallel readdirp with distribute xlator*

Currently the directory listing gets slower as the number of 
bricks/nodes increases in a volume, though the file/directory numbers 
remain unchanged. With this feature, the performance of directory 
listing is made mostly independent of the number of nodes/bricks in the 
volume. Thus scale doesn't exponentially reduce the directory listing 
performance. (On a 2, 5, 10, 25 brick setup we saw ~5, 100, 400, 450% 
improvement consecutively)

To enable this feature:
# gluster volume set <VOLNAME> performance.readdir-ahead on
# gluster volume set <VOLNAME> performance.parallel-readdir on

To disable this feature:
# gluster volume set <VOLNAME> performance.parallel-readdir off

If there are more than 50 bricks in the volume it is good to increase 
the cache size to be more than 10Mb (default value):
# gluster volume set <VOLNAME> performance.rda-cache-limit <CACHE SIZE>

*md-cache can optionally -ve cache security.ima xattr*

 From kernel version 3.X or greater, creating of a file results in 
removexattr call on security.ima xattr. This xattr is not set on the 
file unless IMA feature is active. With this patch, removxattr call 
returns ENODATA if it is not found in the cache.

The end benefit is faster create operations where IMA is not enabled.

To cache this xattr use,
# gluster volume set <VOLNAME> performance.cache-ima-xattrs on

The above option is on by default.

*Added support for CPU extensions in disperse computations*

To improve disperse computations, a new way of generating dynamic code 
targeting specific CPU extensions like SSE and AVX on Intel processors 
is implemented. The available extensions are detected on run time. This 
can roughly double encoding and decoding speeds (or halve CPU usage).

This change is 100% compatible with the old method. No change is needed 
if an existing volume is upgraded.

You can control which extensions to use or disable them with the 
following command:
# gluster volume set <VOLNAME> disperse.cpu-extensions <type>
    Valid values are:
     none: Completely disable dynamic code generation
     auto: Automatically detect available extensions and use the best one
     x64: Use dynamic code generation using standard 64 bits instructions
     sse: Use dynamic code generation using SSE extensions (128 bits)
     avx: Use dynamic code generation using AVX extensions (256 bits)

The default value is 'auto'. If a value is specified that is not 
detected on run-time, it will automatically fall back to the next 
available option.

*Bugs addressed*

Bugs addressed since release-3.9 are listed in our full release notes [2].

[1] Release 3.10.0 packages: 
https://download.gluster.org/pub/gluster/glusterfs/3.10/3.10.0/

[2] Full release notes for 3.10.0: 
https://github.com/gluster/glusterfs/blob/release-3.10/doc/release-notes/3.10.0.md