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A method for changing data cache size dynamically during read operation to avoid wrap turn effect on tape file system.

IP.com Disclosure Number: IPCOM000235593D
Publication Date: 2014-Mar-11
Document File: 1 page(s) / 14K

Publishing Venue

The IP.com Prior Art Database

Abstract

To prevent and/or reduce data reading delays at wrap turns in the tape drive of a file system.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 51% of the total text.

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A method for changing data cache size dynamically during read operation to avoid wrap turn effect on tape file system.

To prevent and/or reduce data reading delays at wrap turns in the tape drive of a file system.

Disclosed is a data reading method and program for tape drive. It relates to the reading of data from a tape drive and, more specifically, to a method for reading data from a tape in a tape drive used in a file system.

Tape drives can be used in file systems similar to hard disk drives (HDD). Tape drives compatible with Linear Tape-Open (LTO) standards (LTO-5 or later) can be used in file systems. The tape used in LTO tape drives has a plurality of wraps (for example, 80). When data is written to such a tape and the reading of data from a single wrap has been completed, a so-called "wrap turn" operation is required to reverse the traveling direction of the tape and move to read data from the next wrap. One type of file system
is a Linear Tape File System (LTFS). Because data is read continuously from a data drive in LTFS, a so-called read cache function is required to read data from the tape while data accumulated in the buffer is successively transferred to the application. Because a LTFS tape drive with a read cache function cannot read data from a tape during the seconds required to perform the wrap turn operation, the read data during this period simply is transferred from the buffer to an application. Often, the buffer becomes empty and the transfer of data from the buffer is interrupted. Because an LTFS buffer is shared with other peripherals in addition to the host, there is a chance that data transfer will be interrupted at each wrap turn. As a result, problems occur related to delays in reading data from LTFS tape drives. Increasing the storage capacity of buffers has been considered as a way of preventing interruptions in the transfer of data from buffers. However, regularly freeing up a large amount of storage capacity for the LTFS is undesirable as the LTFS then monopolizes the resources of the host using the LTFS. Because LTFS is shared w...