Tip of the Day: Some hidden DFSR improvements
There are some well-hidden DFSR supportability improvements in Win2012:
- Dirty shutdown worker progress –
Background - DFSR used a per-volume ESE database to track all file changes in replicated folders on those volumes. DFSR contains code to attempt graceful and dirty recovery of the database after a dirty shutdown
Legacy behavior – DFSR logged DB recovery events, but had long periods of recovery operations with no instrumentation. This lead to customers thinking recovery was stalled or broken
Win2012 behavior - Two new event log messages now appear that describe where the internal repair process stands. The customer and support engineer at least know that DFSR has moved past the detection phase and into the consistency checking and perhaps rebuilding phase
- Performance registry defaults –
Background - DFSR contains registry overrides to control behaviors like the number of files to replicate simultaneously, stage simultaneously, etc.
Legacy behavior - Windows Server 2008 R2 default registry-tuning settings were too conservative
Win2012 behavior - more aggressive settings are now the default in Windows Server 2012 if not overridden in the registry (see here). We also limit UpdateWorkerThreadCount to 63 now to prevent a deadlock
- RODC support for Dfsmgmt.msc –
Background - Dfsmgmt.msc tool behaviors when contacting DCs for changing the topology
Legacy behavior - DFSMGMT.MSC expects all DC's to be writable when creating a DFSR RG or any other AD objects. When it tries to write to an RODC because that domain controller returned from a standard DC Locator query, it fails with an access denied error
Win2012 behavior - Dfsmgmt.msc now requests only writable domain controllers when making DC queries
- Read-only disconnected topology detection –
Background - Dfsmgmt.msc tool contains a topology checking routine to alert administrators when they have created an incomplete (aka "disconnected") DFS replication topology
Legacy behavior - A bridged topology of A <-> B <-> C is not flagged as disconnected when B is a read-only replicated folder
Win2012 behavior – The topology checker code now understands the bridged read-only replicated folder scenario and appropriately warns the administrator when detected
- 4412 conflict event data –
Background - DFSR uses a series of conflict resolution algorithms to detect file collisions and appropriately handle a winning and losing file
Legacy behavior – The 4412 event did not contain enough information to assist customers in troubleshooting unexpected collisions
Win2012 behavior - The 4412 event message now contains an additional field of Partner Member ID that lists the winning server's identity
- Editions restrictions removed –
Background - Windows Server 2012 removes the Enterprise edition and now contains only the Standard and Datacenter editions
Legacy behavior – DFSR cross-file Remote Differential Compression (RDC) support ties to the server edition being Enterprise or Datacenter. DFSR Cluster support ties to Enterprise or Datacenter editions as well
Win2012 behavior - All edition checks removed and Windows Server 2012 has full DFSR capabilities even in Standard edition
- Initial sync to RO with preexisting data –
Background - Read-only (RO) replicated folders are always non-authoritative and do not allow local changes by use of an IO-blocking filter driver named dfsrro.sys. Customers are encouraged to pre-seed data before initial sync, meaning that data can already exist when DFSR is configured on two or more servers
Legacy behavior - Windows Server 2008 R2 SP1 introduced a regression where initial sync from RW to RO does not overwrite file differences on the RO. This leads to data inconsistencies in the replication groups, as these files will never be right on RO servers unless they are later modified again on the RW
Win2012 behavior – Fixed
- Other stuff
Added support for Dedup, FCI, and DAC file modifications –
DFSR allows reparse point replication rules to support replicating the new IO_REPARSE_TAG_DEDUP tag
FCI no longer re-writes unchanged data to the alternate data stream on files during classification passes, which would lead to DFSR replication
DFSR modified to understand changes made to security APIs for DAC
File creation conflict algorithm - Windows Server 2012 changes one of the file conflict resolution algorithms used from first creator wins to last creator wins
Keep alive Support added for huge files - Windows Server 2012 now correctly allows very large (multi-hundred GB) files to complete computation of RDC signatures before the RPC server connection times out
Integrated recent Win2008 R2 DCRs – (https://support.microsoft.com/kb/2607047 & https://support.microsoft.com/kb/2663685 are the biggies)
ReFS - DFSR does not support ReFS volumes, as this new file system removes many critical data types used or supported by DFSR, such as streams, sparse files, compressed files, 8.3 names, extended attributes, etc.
CSV - Just like Windows Server 2008 R2, DFSR in Windows Server 2012 does not support Cluster Shared Volumes (CSV)