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A method for high speed recovery of high resolution tape directory on linea tape

IP.com Disclosure Number: IPCOM000018645D
Original Publication Date: 2003-Jul-30
Included in the Prior Art Database: 2003-Jul-30
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Abstract

Linear tape has a tape directory information regarding written data on the tape medium in order to provide a fast access to desired target data on the tape. The directory information is mostly available, but once it is corrupted somehow, it usually takes a lot of time to recover the information, because all written data must be read. This method provides a fast recovery method of tape directory on linea tape medium by selecting the fastest way from among three different recovery ways.

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A method for high speed recovery of high resolution tape directory on linea tape

  Every written data unit on tape contains a distributed tape directory information (a part of tape directory). End of data (EOD) which is written as last data on tape also contains almost all tape directory information just before the written EOD. These tape directory information are written on tape itself and have higher resolution information than that saved in nonvolatile cartridge memory.

There are three ways to rebuild the tape directory, (1) using the distributed tape directory which is written in every data unit, (2) using the tape directory written in EOD, and (3) directly rebuild the tape directory while reading. Estimate the recovery time for each way. At this time, the tape directory which should be recovered is prior to the target dataset which is specified by host computer.

1. Time estimation for recovery using the distributed tape directory At a locate or space SCSI command, determine a wrap number of the target using nonvolatile cartridge memory tape directory, and also determine the minimum required number of entries of the high resolution tape directory up to the target data. If there are enough data on the next or later wraps for the recovery, add an estimated time in order to read the data to the recovery time. If there are not enough data on the wraps, this recovery way should not be selected. When this way is available, add (1) an estimated time in order to find a valid data and (2) an estimated time in order to move to the target wrap to the recovery time. The total time is the estimated time for this recovery way. The recovery way is shown in Figure 1.

2. Time estimation for recovery using EOD If it i...