 Virtual Branches   from     ACORN Software   "storage in a nutshell"      Virtual Branches   Product Description       G VirtualBranches provides a "disk farm in a box". For a wide variety of  F Optical and CDROM data libraries each I/O surface in the data library I appears to be an individual disk. No special action need be taken by the  G user of the disk, other than to mount it, in order to access data. The  G 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.  C VirtualBranches provides two unique features available in no other  	 product:  6   *	Correct MSCP serving of robot-served disk drives.    *	Fragmentation Avoidance.         Product Availability  G VirtualBranches V2.2-1 is available for a 45-day free trial and may be  B freely downloaded and installed via FTP or Gopher. Documentation, E supplied in machine readable form with the installation kits, may be  D printed at will. If this is not convenient, then hard copies of the G documentation are available from Acorn Software. If downloading is not  H 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   E VirtualBranches disks are NOT MSCP served to a cluster. Rather, each  E cluster node has a server which communicates with the current master  E node (a master node is one which can control the robot inside a data  % library) to coordinate MSCP traffic.  I This is necessary because of a limitation in MSCP serving. If sufficient  D load is reached on MSCP served disks, and I/O to those disks cannot H complete quickly enough, the underlying cluster communications services E drops the connection to that served disk and attempts to rebuild it,  I putting all the mounted disks into mount verify, thus further increasing  D the I/O load at the MSCP level and causing a positive feedback that E ultimately requires the rebooting of the entire cluster to clear the  A problem. If the VirtualBranches disks were MSCP served (as other  D products have them including Digital's OSMS), VirtualBranches would " suffer from this problem as well. C Thanks to the unique design of VirtualBranches, no MSCP traffic is  G queued for a VirtualBranches disk unless the associated media is known  C to be physically resident in a drive. Thus, cluster operation will  @ remain stable with VirtualBranches regardless of the load level.    H ------------------------------------------------------------------------  < Copyright (c) 1996 Acorn Software, Inc. All rights reserved 