NDLI: Why specialized disks for composite operations may be unnecessary

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Volume 38, Issue 5, December 2010

A novel architecture for conversion of binary to single digit double base numbers

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Adding concurrency in python using a commercial processor's hardware transactional memory support

Why specialized disks for composite operations may be unnecessary

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Volume 38, Issue 4, September 2010

Volume 38, Issue 3, June 2010

Volume 38, Issue 2, May 2010

Volume 38, Issue 1, March 2010

Why specialized disks for composite operations may be unnecessary

Content Provider	ACM Digital Library
Author	Thomasian, Alexander
Abstract	Disk arrays with erasure coding such as RAID5 and RAID6 incur four and six disk accesses respectively for updating data and check blocks. The small write penalty can be reduced by the Read-Modify-Write (RMW) composite operations to update data and associated check blocks. The Disk Architecture with Composite Operation (DACO) is a proposal to eliminate the disk rotation associated with RMWs, by using a complex read/write head, which allows the writing of a block immediately after reading and modifying it without needing an extra disk rotation. We argue that the extra cost associated with DACO may not be justifiable, because it is not expected to have a significant impact on RAID performance. Furthermore an XOR capability is still required at the disk array controller for reconstructing missing data blocks. A duplexed Nonvolatile Storage (NVS) cache at the disk array controller provides the same reliability as magnetic disks and allows fast writes, i.e., writing to disk is considered completed as soon as data is written onto NVS. Deferring the destaging of data blocks from NVS allows these blocks to be be overwritten, obviating unnecessary disk writes. This also allows neighboring dirty blocks to be destaged in batches, so that a higher disk access efficiency is attained. Disks with multiple arms can also be used to make the processing of RMW requests more efficient, while disks with multiple R/W heads on one arm have little effect on RMW requests. In addition there are alternative methods to update check blocks, such as floating parities, parity logging, the reconstruct write method, log structured arrays, and variable scope parity protection.
Starting Page	20
Ending Page	27
Page Count	8
File Format	PDF
ISSN	01635964
DOI	10.1145/1978907.1978912
Journal	ACM SIGARCH Computer Architecture News (CARN)
Volume Number	38
Issue Number	5
Language	English
Publisher	Association for Computing Machinery (ACM)
Publisher Date	1981-04-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Content Type	Text
Resource Type	Article

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