Browse Prior Art Database

Dynamic Sparing Of A Fixed Head

IP.com Disclosure Number: IPCOM000048674D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 72K

Publishing Venue

IBM

Related People

Chang, HK: AUTHOR [+3]

Abstract

Assuming a fixed head device has 32 fixed heads (heads 0 through 31). 30 heads (heads 0 through 29) may be used immediately by the user. The remaining 2 heads (heads 30 and 31) are spared. All 32 fixed heads are good, and their tracks have been surface analyzed.

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Dynamic Sparing Of A Fixed Head

Assuming a fixed head device has 32 fixed heads (heads 0 through 31). 30 heads (heads 0 through 29) may be used immediately by the user. The remaining 2 heads (heads 30 and 31) are spared. All 32 fixed heads are good, and their tracks have been surface analyzed.

When one of the 30 fixed heads becomes defective, it is not capable to read or to write any data on its track. After a failure to a defective fixed head has been diagnosed, a sparing algorithm can be involved as follows:
(1) Record the address of the defective head in an area

accessible by the device. Use a spare head as its

replacement.
(2) Invalidate the control storage area that keeps the

defective head information of the device.
(3) Rebuild the data of the track that has the defective

head on a track, replacing it.

In a typical Count-Key-Data architecture (Fig. 1) with a storage director and a string of devices controlled by a controller (Fig. 2), the defective head information may be recorded in the Home Address area of head 31. When a SI0 is sent by a CPU channel to the storage director, the latter will check its control storage to see if the defective head information of this fixed head device has been validated or not.

If the information is not validated in the control storage, such as the case of an initial power on or after a defective head sparing, the storage director will present retry status, disconnect from such as the channel, switch to fixed head 31, read its Home Address area, extract the defective head information from the Home Address area, validate the information in the control storage, reconnect to the channel, and continue normal...