| Appendix C. Recovering Data Guarantees | ||
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| Appendix C. Recovering Data Guarantees | ||
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Table of Contents
NearStore VTL appliances buffer both disk and compact flash writes for improved performance (as do tape devices). After data is on the NearStore VTL disks and compact flash, user data can be recovered in the event of failures such as reboot, power failure, disk failure, or compact flash failure. The differences in the nature of the information written to disk and compact flash results in two different types of data recovery guarantees: the ability to recover data after a reboot, including ones due to power failure, and recovery of data after the failure of the compact flash.
The SCSI standard defines a number of SCSI commands that are required to flush the buffers to media before the device can return a successful status. NearStore VTL appliances comply with these requirements. The commands are: WRITE_FILEMARKS, SPACE, LOCATE, LOAD/UNLOAD and REWIND. After receiving one of these commands, all “tape-image” data received by the VTL appliance before the command, is available in the event of a power failure or reboot (but might not be recoverable after a compact flash failure. See the section called “Recovering Data after a Compact Flash Failure”)
Until one of the SCSI commands trigger a flush, the data in the current file is not guaranteed to be available in the event of a power failure or reboot.
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| Appendix B. Replacing a NearStore VTL Head |  |
Recovering Data after a Compact Flash Failure |
Copyright © 1994-2006, Network Appliance, Inc. All rights reserved.
Part number 210–01204_A0
Preliminary edition
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