A Welcome Appliance for NT/Unix Administrators

Hands On Review

With the amount of hype in the computer industry today, exemplified by snappy product names, not many companies refer to their products as an "appliance." This review looks at a network file server from Network Appliance that has a decidedly unglamorous name: F720 filer.

Network Appliance (NetApp) produces a line of networked storage servers, or filers, that combine flexible storage with some elegant proprietary designs, that offer some appealing features when combined. Foremost of these is an ability to appear as NT storage to any Windows client, and simultaneously appear as Unix storage to any Unix machine.

We tested a lightly configured NetApp F720 filer, which is the low end of the product line. The filer consists of two disk shelves and one substantial "server" unit, all rack-mountable. The disk shelves used 9.1 GB SCSI disks and modular power supplies in identically packaged units. Our test unit had 13 drives, for a total raw capacity of 118.3 GB. Typically, the filer would use Fiber Channel - Arbitrated Loop (FC-AL) disk drives of either 9 or 18 GB capacity each, partly for the faster data bus and partly for the larger number of devices – 128 -- that FC-AL supports.

The filer's server portion includes 256 MB of RAM, a substantial but curiously unidentified RISC processor, 8 MB of Non Volatile Random Access Memory (NVRAM), one FC-AL and two SCSI channels and an accessible chassis layout that places the motherboard and expansion cards on a roll-out tray. The Data ONTAP (Open Network Technology for Appliance Products) operating system is preinstalled, making the setup process a matter of following a couple of clear diagrams for SCSI cable connections and the much smaller Environmental Monitoring Unit (EMU) cables, and plugging in the network cable.

The control interface is a standard nine-pin serial connector to which we connected a link terminal. Control can also be accomplished through telnet, but since the filer must first be educated as to its network identity, a terminal or PC is needed for the setup phase.

As our NT representative, we set up an IBM Netfinity 5500 server, powered by a 400 MHz Pentium II and running Microsoft Windows NT Server 4.0 with Service Pack 4. For Unix operations, we installed the Red Hat distribution of Linux 5.2 on a Dell PowerEdge 2200 server, using a Pentium II/266 CPU. All server-to-server network connections were made through a 3Com 100BaseT switch, with client connections available at 10BaseT.

Initial Configuration
Upon initial power up, the filer went through a fairly standard set of POST tasks to verify RAM, disk status and so forth. Then the filer requested its TCP/IP address information -- as expected -- but with interesting additional requests for the network name of both the gateway and the administration host. A quick check of documentation verified our guess that the administration host was whichever computer we wanted to designate as the primary controller of the filer. The setup dialogue also asks if the included Domain Name System (DNS) and Network Information System (NIS) services are desired, then goes into the disk configuration choices.

Network Appliance has taken advantage of the design latitude available for a product of this type to maximize performance, stability and security. The designers created a proprietary file system, the Write Anywhere File Layout (WAFL), that encompasses three basic design requirements: It needed to integrate well with a RAID system, it must be able to grow dynamically as new disks are added, and it should not require time consuming consistency checks. The proprietary file system adds two practical benefits to the filer’s operation: the use of RAID 4 for disk redundancy and the facility of Snapshots, which are automatic, online, read-only copies of the entire file system.

The Network Appliance implementation of RAID 4 stripes data across all of the disks except one, which is used as the parity disk. Corruption of any data area, or even the failure of an entire disk, produces an on-the-fly rewrite of the lost data until the bad area or disk is replaced. With most file systems, the parity disk causes a performance bottleneck as every write operation to a stripe necessitates a corresponding but uncoordinated write to the parity disk. To make matters worse the newly written stripes may be scattered over the array causing time consuming seeks.

WAFL minimizes these effects by writing multiple blocks to the same stripe whenever possible and by writing to adjacent stripes instead of scattered locations. The single parity disk allows additional disks to be added to the array as needed, where they are seamlessly integrated into the system, something not possible in a RAID 5 configuration.

The Snapshot facility is a second major benefit of this file system design. At user selected intervals, the filer automatically copies the entire file system in just a few seconds. This consumes an insignificant amount of disk space -- 128 bytes -- until a user deletes or modifies data in the active file system. When this happens, the Snapshot still points to the original data block while the file system points to the new data.

Space permitting, up to 20 Snapshots and their associated blocks may be kept on-line, but the amount and duration depend on how much activity there is and how large the files are. Most typical business users might only add or modify 500 K[B] to 1 MB in a day and maintain it for weeks, but a CAD or 3-D rendering business that routinely and frequently replaces very large files may be able to maintain Snapshots for less than a day.

Making Unix and NT Live Together
One of the most daunting problems that face filers is file locking. Unix, through its Network File System (NFS) and Windows, through the Common Internet File System (CIFS), treat this issue very differently. Largely due to the checkered development history of Unix, it is not unusual for an application to access a file without checking for the existence of another client’s lock, or to request a lock itself. Under CIFS, file locking is routine, and applications normally use and look for locks. The consequences of an NFS client violating a CIFS-enforced lock can include corruption of the file, hanging of the accessing application and crashing of the client machine.

To address this problem, Network Appliance created SecureShare software as an integral part of the filer operating system. SecureShare acts to enforce CIFS locks, even on NFS clients, so all parties respect existing file locks. SecureShare will allow NFS clients to interrupt the "opportunistic lock", or oplock, that a CIFS client may leave on a file that it is not actively using.

We took a very straightforward approach to testing this capability. We attempted to simultaneously open and manipulate the same file from our Linux and an NT machines. When working with a compressed archive using Zip and WinZip, we received error messages that were new to us, but were consistent with locking conflicts. An open text document in Microsoft Word could be opened and manipulated from the Linux client, but when an attempt was made to save the file, we received the message, "Can't open file for writing". When the same test was done with Vi and Notepad as the working applications, the Linux machine did make the changes, seemingly without problems.

The final element of the F720 is a Web-based administration facility. Our only quibble here is that there is not a great deal of control capability available through this interface. The interface is primarily an on-line manual and a compact monitoring screen. Perhaps the idea here was to offer thorough access to, and definitions of, all of the possible commands and their syntax, which could then be executed through a telnet session.

Although the issues that go into the design and creation of this system are complex, the resulting machine should be absolutely mundane in its operation. Our testing operations on the NetApp F720 filer left us with only good impressions. The setup process was admirably clear and quick, the F720 filer’s operations were transparent to all accessing machines and it behaved like a machine most administrators would feel comfortable trusting their company’s critical data to.

Even an accidental disconnection of half of the filer’s power supply and the removal of an operating disk did nothing to interrupt the filer’s operation.

Networked storage represents a healthy investment for any enterprise. Based on the design, quality hardware, and ease-of-use we found in the F720, we suggest that any company with a combined Unix and NT environment that needs storage capacity in the range of this system should put NetApp’s line on their short list to consider.

Network Appliance F720
Network Appliance
Santa Clara, Calif.
(800) 44-FILER
(888) 4-NETAPP (current customers)

Price: All F700 filer models are available from Network Appliance and through industry VARs and resellers. Pricing for the F720 starts at $19,950; the F740 starts at $39,950 and the F760 starts at $79,950.

+ Easy to configure
+ Integrates into a network seamlessly
+ Excellent for environments with Windows NT and Unix shared file access
- Web administration tool is limited in capability

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