|
Here is a cut and paste of an IBM doc on this subject: IBM Software Technical Document __________________________________________________________________ /s_dir/slkbase.nsf/1ac66549a21402188625680b0002037e/e4899b4c32c9116f862565c2007cf565?OpenDocument&ExpandSection=1 - _Section1/s_dir/slkbase.nsf/1ac66549a21402188625680b0002037e/e4899b4c32c9116f862565c2007cf565?OpenDocument&ExpandSection=1 - _Section1Document Information __________________________________________________________________ Document Title Why Damage Can Occur on Raid-5 or Mirrored Drives Document Description Question: Why would I get damaged objects on my system that has a form of data protection running on it? This could be system-level mirroring or drive-level RAID-5 protection. Answer: The reason that damaged objects can occur is that the basic concept behind these techniques is to improve system availability (for example, keep the system up) and recoverability (for example, prevent a loss of data) when disk drive failures occur. If a disk drive fails or has a problem, I/O operations are suspended to it and the system continues to run. When you next try and access the failed disk drive, with mirroring the data is read from the failed drive's mirrored copy and with RAID-5 the data is rebuilt from the parity set contained on the other RAID-5 drives. As an extra benefit to availability and recoverability, they also offer very good data integrity, but it is not guaranteed to be 100 percent. The reason for this is because the system is reliant on either the hardware or software detecting a problem. When hardware sees a problem, the system functions like described above. This is how most data integrity is maintained, and with the newer hardware with more modern (robust) error detection techniques, this is even better. As an example of how a damaged object could occur, consider the following scenario: 1 A disk drive has a problem and it damages an object internally. The hardware somehow doesn't detect that this problem has occurred so the disk drive still stays available. 2 The system then requests and reads that object onto the system (main memory) for processing. 3 If software does not detect the problem with the object on the system, that damaged object could be written back out to disk. With mirroring, both mirrored disk drives would then have copies of the damaged object and with RAID-5, the parity set would be updated with the information in the damaged object The AS/400 Advanced Backup and Recovery Guide states the following: Mirrored protection does not protect your system from damage to objects that occurs for reasons other than a DASD failure. For example, objects may be damaged if your system ends abnormally due to a power failure. __________________________________________________ Kirk Goins IBM Certified iSeries Technical Solutions Expert IBM Certified Designing IBM e-Business Solutions Pacific Information Systems - An IBM Premier Business Partner 503-674-2985 kirkg@pacinfosys.com -----Original Message----- From: Art Tostaine, Jr. [mailto:art@link400.com] Sent: Thursday, August 29, 2002 2:08 PM To: midrange-l@midrange.com Cc: Barry Oppenheim Subject: Raid problems A customer of mine has those BCC drives that were talked about a couple of months ago. One of them failed and the raid set showed UNPROTECTED. BCC sends new drive overnight (they wouldn't replace same day like IBM would). They send Decision Data to replace it. EXCEPT, we have tons of damaged objects. How can objects get damaged if the disks are protected by RAID. Customer called IBM support to talk about this and they say occasionally damaged objects can happen, even with Raid. Has anyone else experienced this? P.S. My customer may chime in here as he wanted the URL on how to join this list. _________________ Art Tostaine, Jr. CCA, Inc. Jackson, NJ 08527 _______________________________________________ This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list To post a message email: MIDRANGE-L@midrange.com To subscribe, unsubscribe, or change list options, visit: http://lists.midrange.com/cgi-bin/listinfo/midrange-l or email: MIDRANGE-L-request@midrange.com Before posting, please take a moment to review the archives at http://archive.midrange.com/midrange-l.
As an Amazon Associate we earn from qualifying purchases.
This mailing list archive is Copyright 1997-2024 by midrange.com and David Gibbs as a compilation work. Use of the archive is restricted to research of a business or technical nature. Any other uses are prohibited. Full details are available on our policy page. If you have questions about this, please contact [javascript protected email address].
Operating expenses for this site are earned using the Amazon Associate program and Google Adsense.
midrange.com
