student guide.pdf

More documents

Recommendations

Info

Copyright © 2005 EMC Corporation. Do not Copy - All Rights Reserved. Symmetrix Fundamentals Host Data Access to Symmetrix Data © 2005 EMC Corporation. All rights reserved. Symmetrix Foundations - 48 Symmetrix Foundations - 48
Copyright © 2005 EMC Corporation. Do not Copy - All Rights Reserved. Read Operations Read Hit Read Miss Channel Director Channel Director Global Memory Global Memory Disk Director Disk © 2005 EMC Corporation. All rights reserved. Symmetrix Foundations - 49 Read Hit In a Read hit operation, the requested data resides in global memory. The channel director transfers the requested data through the channel interface to the host and updates the global memory directory. Since the data is in global memory, there are no mechanical delays due to seek and latency. Read Miss In a read miss operation the requested data is not in global memory and must be retrieved from a disk device. While the channel director creates space in the global memory, the disk director reads the data from the disk device. The disk director stores the data in global memory and updates the directory table. The channel director then reconnects with the host and transfers the data. Because the data is not in global memory, the Symmetrix system must search for data on the disk and then transfer it to the channel, this adds seek and latency times to the operation. Symmetrix Foundations - 49
Page 1 and 2: Copyright © 2005 EMC Corporation.
Page 47: Copyright © 2005 EMC Corporation.
Page 57: Copyright © 2005 EMC Corporation.

student guide.pdf

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?