Virtual Branches from ACORN Software "storage in a nutshell" Virtual Branches Product Description VirtualBranches provides a "disk farm in a box". For a wide variety of Optical and CDROM data libraries each I/O surface in the data library appears to be an individual disk. No special action need be taken by the user of the disk, other than to mount it, in order to access data. The user simply reads and write data, VirtualBranches takes care of moving media to and from the physical drives in the data library while providing access to the entire contents of the data library. VirtualBranches provides two unique features available in no other product: * Correct MSCP serving of robot-served disk drives. * Fragmentation Avoidance. Product Availability VirtualBranches V2.2-1 is available for a 45-day free trial and may be freely downloaded and installed via FTP or Gopher. Documentation, supplied in machine readable form with the installation kits, may be printed at will. If this is not convenient, then hard copies of the documentation are available from Acorn Software. If downloading is not possible or is not convenient, then VirtualBranches may be ordered from Acorn Software on most popular media (TK50, 4mm, 8mm, and MO). Price List Virtual Branches and MSCP Serving VirtualBranches disks are NOT MSCP served to a cluster. Rather, each cluster node has a server which communicates with the current master node (a master node is one which can control the robot inside a data library) to coordinate MSCP traffic. This is necessary because of a limitation in MSCP serving. If sufficient load is reached on MSCP served disks, and I/O to those disks cannot complete quickly enough, the underlying cluster communications services drops the connection to that served disk and attempts to rebuild it, putting all the mounted disks into mount verify, thus further increasing the I/O load at the MSCP level and causing a positive feedback that ultimately requires the rebooting of the entire cluster to clear the problem. If the VirtualBranches disks were MSCP served (as other products have them including Digital's OSMS), VirtualBranches would suffer from this problem as well. Thanks to the unique design of VirtualBranches, no MSCP traffic is queued for a VirtualBranches disk unless the associated media is known to be physically resident in a drive. Thus, cluster operation will remain stable with VirtualBranches regardless of the load level. ------------------------------------------------------------------------ Copyright (c) 1996 Acorn Software, Inc. All rights reserved