2006-07-27 11:16:55 UTC
I am currently deploying two servers (Windows 2003 R2) that will
be used as file servers as well as PostgreSQL servers.
One of the server will be the main server, the other one a backup
server (no load-balancing, only an easy-recoverage solution).
The goal is to be able to start working quickly after one of the
server fails (after the main server fails actually, since the
backup server is not used).
I already configured a high-availability solution for the file
server part by using the built-in DFS Replication service.
I first thought I would use Slony-I to replicate changes to the
main database on the backup server, but I then realized that I
might use DFS Replication for that.
The point is that I am not sure that it will work.
Documentation about DFS Replication is not very talkative (IMHO),
I have to little knowledge of PostgreSQL's file handling to know
if it will work or not.
I have compiled some informations about DFS Replication from
Microsoft"s web site. Could you PostgreSQL gurus tell me whether
using this replication mechanism is a good idea or not ?
The main advantage for me is that I will not need to configure 2
replication systems (one for the files, on for the DBs). I would
only need to maintain one of them !
Here is the documentation I got, thanks a lot for reading me to
this point ! :
"DFS Replication, the successor to the File Replication service
(FRS) introduced in Windows 2000 Server operating systems, is a
new, state-based, multimaster replication engine that supports
replication scheduling and bandwidth throttling. DFS Replication
uses a new compression algorithm known as remote differential
compression (RDC). RDC is a "diff-over-the wire" client-server
protocol that can be used to efficiently update files over a
limited-bandwidth network. RDC detects insertions, removals, and
re-arrangements of data in files, enabling DFS Replication to
replicate only the changed file blocks when files are updated.
DFS Replication uses many sophisticated processes to keep data
synchronized on multiple servers. Before you begin using DFS
Replication, it is helpful to understand the following concepts.
* DFS Replication is a multimaster replication engine. Any change
that occurs on one member is replicated to all other members of
the replication group.
* DFS Replication detects changes on the volume by monitoring the
update sequence number (USN) journal, and DFS Replication
replicates changes only after the file is closed.
* DFS Replication uses a staging folder to stage a file before
sending or receiving it. For more information about staging
folders, see Staging folders and Conflict and Deleted folders.
* DFS Replication uses a version vector exchange protocol to
determine which files need to be synchronized. The protocol sends
less than 1 kilobyte (KB) per file across the network to
synchronize the metadata associated with changed files on the
sending and receiving members.
* When a file is changed, only the changed blocks are replicated,
not the entire file. The RDC protocol determines the changed file
blocks. Using default settings, RDC works for any type of file
larger than 64 KB, transferring only a fraction of the file over
* DFS Replication uses a conflict resolution heuristic of last
writer wins for files that are in conflict (that is, a file that
is updated at multiple servers simultaneously) and earliest
creator wins for name conflicts. Files and folders that lose the
conflict resolution are moved to a folder known as the Conflict
and Deleted folder. You can also configure the service to move
deleted files to the Conflict and Deleted folder for retrieval
should the file or folder be deleted. For more information, see
Staging folders and Conflict and Deleted folders.
* DFS Replication is self-healing and can automatically recover
from USN journal wraps, USN journal loss, or loss of the DFS
* DFS Replication uses a Windows Management Instrumentation (WMI)
provider that provides interfaces to obtain configuration and
monitoring information from the DFS Replication service."
Many thanks for your advices on this !
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