Hardware-Based NFS Servers: Built For Prime-Time Speed Man y factors can determine raw performance of a server. RAID configuration, for example, can have an impact. A poorly configured server with 16 disks can perform worse than a server with only six disks. But generally, more disks mean better performance--writing to many drives simultaneously allows a greater amount of data to be read and written at any one time. However, special attention needs to be paid to the applications that are being hosted by an NFS server. You can tune RAID arrays to serve many smaller files quickly, or they can be configured to serve many larger files quickly. Reliability is a key factor for NFS file servers. Besides assisting in the speed department, RAID can replicate information in times of single-drive failures. Most servers can detect a bad drive and automat ically switch to a drive marked as a hot spare. Invincible Technologies Corp.'s LIFELINE SFT Invincible Technologies LIFELINE SFT server provides a powerful NFS server package with an extremely impressive features list. Its ability to prevent downtime is unparalleled. LIFELINE SFT provides not only redundant components, but two redundant computers as well--a lifeline that makes us feel secure. SFT stands for symmetric fault tolerance. This is critical to the device's ability to maximize uptime while minimizing effort. Say, for instance, that you inadvertently powered down one of LIFELINE SFT's modules, one we'll call Adam. When LIFELINE SFT's redundant computer, Betty, realizes that Adam has stopped talking across their shared SCSI bus, Betty's SFT system springs into action. Betty informs the couple's shared hardware RAID controller that Adam is not working, and she will now be ser ving Adam's file systems. Betty then serves Adam's file systems until Adam is revived. Although this process seems rather simple, it's actually quite complicated. LIFELINE SFT uses a notable solution--which Invincible calls a service--to enable its failover capabilities. A service is defined as any exported directory. Normally there is one service for each file system exported on your server; in the LIFELINE SFT system, every exported file system is exported under its own distinct IP address. When Betty notices that Adam no longer is responding, she takes over Adam's IP addresses and begins serving them as if they were her own. The total downtime to the clients is less than 3 seconds. This technology comes in handy with system maintenance and upgrades. If you want to add RAM to each of your two machines, simply move all of the services onto one machine, then bring down the second one and perform the upgrade. Other than a minor hiccup, your clients won't notice any changes. None of the other systems w e tested in our lab offered anything close to this level of redundancy. LIFELINE SFT offers another advantage. Under normal circumstances, it takes a long time to create a multigigabyte file system. Using Digital Equipment Corp.'s Advanced File System, however, LIFELINE SFT can begin using the file system while the operating system is still initializing it. This lets you get the file system up in an extremely short amount of time. Within a few minutes of adding disks to the RAID array, the system can export them to the network. We found performance to be remarkable, considering the server was busy completing the initialization. Digital's Advanced File System also offers other high-end features, such as online defragmentation. It is difficult to defragment the file system on a Unix system. (Unix systems generally are good about not fragmenting the file system, but sooner or later defragmentation becomes necessary.) To safely cache NFS file writes, LIFELINE SFT server uses a battery-backed RAID cont roller that controls the array of drives. Since both of LIFELINE's machines use the same RAID controller to store their information, if one computer were to stop functioning suddenly, the information recently written to the disk array would still be available. Be cause of the complexity of some aspects of LIFELINE SFT's operation, we got unexpected or unwanted results a few times during testing. We often had to set up the services several times before the SFT system would handle them correctly. This is a problem only when you first set up the server, however, and once it is running the system works well. Overall, Invincible has created a system that provides lots of functionality in a very flexible manner.

Updated April 8, 1997