Riverbed Steelhead EX, Руководство по установке и настройке

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48 Steelhead Appliance Installation and Configuration Guide
Troubleshooting Oplock Issues
Possible Causes

The client is running an old anti-virus software such as McAfee v4.5, the most common type, which
competes with the application for an oplock instead of opening as read-only. The antivirus causes
multiple file opens.

The server has oplocks disabled.
Example
You can open a previously-accessed file in 5 seconds on PC1, but you cannot open the same file under 24
seconds on PC2. If you close the file on PC1, you can open it in 5 seconds on PC2. However, it takes you 24
seconds to open the same file on PC1.
Solutions
Windows Common Internet File System (CIFS) uses oplock to determine the level of safety the OS or the
application has in working with a file. Oplock is a lock that a client requests on a file in a remote server.
An oplock controls the consistency of optimizations such as read-ahead. Oplock levels are reduced when
you make conflicting opens to a file.
To prevent any compromise to data integrity, the Steelhead appliance only optimizes data when a client has
exclusive access to the data.
When an oplock is not available, the Steelhead appliance does not perform application-level latency
optimization but still performs Scalable Data Referencing (SDR) and data compression as well as TCP
optimization. Therefore, even without the benefits of latency optimization, Steelhead appliances still
increase WAN performance, but not as effectively as when application optimizations are available.
To resolve oplock issues:

Upgrade your anti-virus software to the latest version.

Use Filemon (sysinternals) to check for file access.

Enable CIFS Overlapping Opens (by default, this function is enabled). For details, see “CIFS
Overlapping Open Optimization Denies Multi-User Access” on page 49 .

Ensure that the server has oplock enabled by verifying registry settings on Windows servers or the
Filer configuration (for NetApp or EMC servers).

Run a network analyzer such as Riverbed Cascade Pilot, which is fully integrated with Wireshark, and
determine that the server grants oplocks when the client opens a file.

Check whether the client is running an anti-virus software that is scanning the files over the WAN or
that the anti-virus software does not break the oplock.