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Pseudo Skip Write for Devices Which Do Not Support Skip Write

IP.com Disclosure Number: IPCOM000102645D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Vriezen, JJ: AUTHOR

Abstract

An improved method for DASD write operations is described. The improvement applies to those situations where several nearly contiguous DASD sectors are to be written to a disk which does not support "skip-write" operations. The operation is reduced to two I/O operations rather than several or many I/O operations.

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This is the abbreviated version, containing approximately 53% of the total text.

Pseudo Skip Write for Devices Which Do Not Support Skip Write

       An improved method for DASD write operations is
described. The improvement applies to those situations where several
nearly contiguous DASD sectors are to be written to a disk which does
not support "skip-write" operations.  The operation is reduced to two
I/O operations rather than several or many I/O operations.

      Many low-end DASD devices do not support the operation known as
"skip-write."  Skip-write allows the operating system software to
specify that several main store pages are to be written to disk, in
one single I/O operation, but not contiguously on DASD.  The pages
must be located relatively close to one another, but there can be
gaps.  On devices that do support skip write, several nearby
non-contiguous pages can be written in one I/O operation.

      Skip-write is useful in a demand paging system where in one
contiguous range of virtual address space, some pages may reside in
main store with unwritten changes, and others in the range may not be
resident at all.  (It is assumed that contiguous virtual addresses
are, for the most part, stored contiguously on the DASD.)

      This is important, since each disk write takes a considerable
amount of time, and the fewer disk writes needed to satisfy a single
request, the better the overall performance of the system.

      This invention reduces the number of disk operations required
for the devices which do not suppo...