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Technology Stocks : Son of SAN - Storage Networking Technologies -- Ignore unavailable to you. Want to Upgrade?

To: Craig Stevenson who wrote (219)	12/8/1997 11:06:00 AM
From: George Dawson	Read Replies (1) \| Respond to of 4808

Craig, From the literature it also looks like the "guarantee" is relative: "3.6.3 Guarantee Mechanism Applications request guarantees by providing a file descriptor, data rate, duration, and start time. The filesystem calculates the performance available and, if the bandwidth is available, guarantees that the requested level of performance can be met for the given period of time. To make a bandwidth reservation, a user issues a grio_request call on a file. All real-time data accesses are made with standard read and write system calls. Guaranteed rate I/O does not impact the buffer cache, because programs which utilize this mechanism are required to use direct I/O - avoiding the buffer cache. Real-time data may also be accessed in a non-realtime way using only direct I/O calls without GRIO. The knowledge of the available bandwidth for reservation is located in a user level reservation scheduling daemon ggd. The daemon has knowledge of the characteristics and configuration of the disks and volumes on the system (including backplane and SCSI bus throughput), and it tracks both current and future bandwidth reservations. By default, IRIX supports four GRIO streams (concurrent uses of GRIO). The number of streams can be increased to 40 by purchasing the High Performance Guaranteed-Rate I/O-5-40 option or more using the Unlimited Streams option. Note: Disk drivers have been modified to recognize guaranteed rate requests and to schedule them in a real time manner. The disk and volume drivers also export an interface for acquiring their response time and bandwidth characteristics for use by the reservation scheduling module. " It would be a lot easier to make these bandwidth requests if you had some class 1 channels.