Mirroring: Different Strokes

Each of the three available NetWare mirroring products deploys a unique mechanism to synchronize the mirrored servers and to start the secondary server when the primary server fails. StandbyServer 32 makes the disks in a secondary server appear as local disks to the primary server through two interface cards and a cable. NetWare's native disk mi rroring duplicates primary-server data on the secondary server. When the secondary server senses primary-server failure over the network, it reboots and comes up as the primary server.

NetWare SFT III provides the only server mirroring that is nonstop fault-tolerant. You connect two identical s ervers by Mirrored Server Link (MSL) network adapters, which provide a dedicated high-speed communications channel between the servers. NetWare SFT III's Multi Server Engine module synchronizes the two servers so that the disk contents and memory image of each remain identical. The mirrored servers must be identical. When the primary server fails, the secondary server becomes the primary server without any interruption in handling user requests.

With Compaq's Recovery Server Option, two identical servers attach to the same SCSI disk array. If the primary server fails, the SCSI bus switches to the control of the secondary server, which reboots using the OS files and volumes found on the shared disk array. Users experience a brief interruption during the reboot and must reconnect to the server. Disk fault tolerance comes from the mirroring and RAID features provided by Compaq's SCSI controller.

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Feature Comparison: Server-Mirroring Products

                        
VINCA STANDBY-  NETWARE         COMPAQ RECOVERY
                        SERVER 32       SFT III         SERVER OPTION

Unattended fail-over    Yes             Yes             Yes
Nonstop fail-over       No              Yes             No or (no user interruption)
Requires identical      No              Yes             Yes
 secondary server
Requires second         No              Yes             No
NetWare license
Allows partial server   Yes             No              Yes
 mirroring (selected
 volumes)
NOS support             NetWare 4.x     NetWare         NetWare 4.x and
                        and 3.x         4.x             3.x, Windows NT