Troubleshooting guide

1-4
Cisco Wide Area Application Services Configuration Guide
OL-26579-01
Chapter 1 Configuring File Services
Overview of File Services Features
• Strict CIFS behavior for intra-site—Users of the same cache are always guaranteed standard, strict
CIFS coherency semantics.
• Cache validation on CIFS open—In CIFS, the File Open operation is passed through to the file
server. For coherency purposes, WAAS software validates the freshness of the file on every file
open, and invalidates the cached file if a new version exists on the file server.
WAAS software validates data by comparing the time stamp of a file in the cache to the time stamp
of the file on the file server. If the time stamps are identical, the cached copy on the Edge WAE is
considered valid and the user is permitted to open the file from the Edge WAE cache.
If the time stamps are different, the Edge WAE removes the file from its cache and requests a fresh
copy from the file server.
• Proactive cache updating—WAAS software supports the use of change notifications in CIFS
environments as a way to keep cached data on the Edge WAEs up-to-date.
When a client makes a change to a directory or file, the Edge WAE sends a change notification to
the file server. The file server then sends to all the Edge WAEs a change notification that includes a
list of the modified directories and files. Upon receiving the change notification, each Edge WAE
checks its cache and invalidates the directories and files listed in the notification, and then updates
its cache with the latest versions.
For example, if a user edits an existing Word document and saves the changes to the Edge WAE
cache, the Edge WAE sends a change notification to the file server so it knows that the file has been
modified. The Edge WAE then sends the changed sections to the file server, and the file server
proactively sends change notifications to the other Edge WAEs in the network. These Edge WAEs
then update their cache so the file is consistent across all access points.
This process also applies when you rename a directory, add a new subdirectory, rename a file, or
create a new file in a cached directory.
• Flush on CIFS close—In CIFS, the File Close operation forces all write buffers to be flushed to the
file server, and the Close request is only granted after all updates have been propagated to the file
server. From a coherency standpoint, the combination of validate on file open and flush on file close
ensures that well-behaved applications, such as Microsoft Office, operate in session semantics. The
Open, Lock, Edit, Unlock, and Close commands are guaranteed to work correctly on the WAAS
network.
• Age-based validation on directories (CIFS)—Directories are associated with a preconfigured age.
When the age expires, the Edge WAE cache revalidates the directory.
When a user first attempts to view the contents of a directory, the Edge WAE enables the file server
to perform the authorization check using the directory’s access control list (ACL), which contains
the user and group permissions. The Edge WAE monitors which directories the user has accessed
and whether the file server permitted that access. If the user tries to access the same directory again
during a short period of time (aging period), the Edge WAE does not contact the file server and
instead uses the cached permissions to determine if the user should be provided access. After the
aging period expires, the Edge WAE contacts the file server to refresh the cached permission of the
user.
This authorization process prevents users from accessing directories and files in the cache that they
do not have permission to access on the file server.