anchor.diff:  You will likely find references to the HLog in documentation tailored to these older versions.
   ====
   
  -The WAL resides in HDFS in the _/hbase/WALs/_ directory (prior to HBase 0.94, they were stored in _/hbase/.logs/_), with subdirectories per region.
  -
  -For more general information about the concept of write ahead logs, see the Wikipedia link:http://en.wikipedia.org/wiki/Write-ahead_logging[Write-Ahead Log] article.
  +The WAL resides in HDFS in the _/hbase/WALs/_ directory, with subdirectories per region.
  +
  +For more general information about the concept of write ahead logs, see the Wikipedia
  +link:http://en.wikipedia.org/wiki/Write-ahead_logging[Write-Ahead Log] article.
  +
  +
  +[[wal.providers]]
  +==== WAL Providers
  +In HBase, there are a number of WAL imlementations (or 'Providers'). Each is known
  +by a short name label (that unfortunately is not always descriptive). You set the provider in
  +_hbase-site.xml_ passing the WAL provder short-name as the value on the
  +_hbase.wal.provider_ property (Set the provider for _hbase:meta_ using the
  +_hbase.wal.meta_provider_ property).
  +
  + * _asyncfs_: The *default*. New since hbase-2.0.0 (HBASE-15536, HBASE-14790). This _AsyncFSWAL_ provider, as it identifies itself in RegionServer logs, is built on a new non-blocking dfsclient implementation. It is currently resident in the hbase codebase but intent is to move it back up into HDFS itself. WALs edits are written concurrently ("fan-out") style to each of the WAL-block replicas on each DataNode rather than in a chained pipeline as the default client does. Latencies should be better. See link:https://www.slideshare.net/HBaseCon/apache-hbase-improvements-and-practices-at-xiaomi[Apache HBase Improements and Practices at Xiaomi] at slide 14 onward for more detail on implementation.
  + * _filesystem_: This was the default in hbase-1.x releases. It is built on the blocking _DFSClient_ and writes to replicas in classic _DFSCLient_ pipeline mode. In logs it identifies as _FSHLog_ or _FSHLogProvider_.
  + * _multiwal_: This provider is made of multiple instances of _asyncfs_ or  _filesystem_. See the next section for more on _multiwal_.
  +
  +Look for the lines like the below in the RegionServer log to see which provider is in place (The below shows the default AsyncFSWALProvider):
  +
  +----
  +2018-04-02 13:22:37,983 INFO  [regionserver/ve0528:16020] wal.WALFactory: Instantiating WALProvider of type class org.apache.hadoop.hbase.wal.AsyncFSWALProvider
  +----
  +
   
   ==== MultiWAL
   With a single WAL per RegionServer, the RegionServer must write to the WAL serially, because HDFS files must be sequential. This causes the WAL to be a performance bottleneck.
  
positive.code: There is no way to disable the WAL for only a specific table.
  
  WARNING: If you disable the WAL for anything other than bulk loads, your data is at risk.
  
  [[regions.arch]]
  == Regions
  
negative.code: mid-write. If entries in this last block were added with new dictionary entries but we failed persist the amended
  dictionary because of an abrupt termination, a read of this last block may not be able to resolve last-written entries.
  
  [[wal.durability]]
  ==== Durability
  It is possible to set _durability_ on each Mutation or on a Table basis. Options include:
  
   * _SKIP_WAL_: Do not write Mutations to the WAL (See the next section, <<wal.disable>>).
   * _ASYNC_WAL_: Write the WAL asynchronously; do not hold-up clients waiting on the sync of their write to the filesystem but return immediately; the Mutation will be flushed to the WAL at a later time. This option currently may lose data. See HBASE-16689.
   * _SYNC_WAL_: The *default*. Each edit is sync'd to HDFS before we return success to the client.
   * _FSYNC_WAL_: Each edit is fsync'd to HDFS and the filesystem before we return success to the client.
  
  Do not confuse the _ASYNC_WAL_ option on a Mutation or Table with the _AsyncFSWAL_ writer; they are distinct
  options unfortunately closely named
  
  [[wal.disable]]
  ==== Disabling the WAL
  
  