How Does AIX Deal With Bad Blocks

April 4th, 2009

The biggest concern for any organization using a server is data integrity. The various solutions like Network Attached Storage, Storage Area Networks, high availability servers, online data backup and disaster recovery solutions are among the available solutions.

Apart from the third party available solutions for protecting Physical Volumes. The native data protection solutions provided by AIX are:

  1. Bad Block Relocation.
  2. Mirroring.
  3. Quorum Checking.

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Here in the article we’ll be discussing Bad Block Relocation.

Bad Block Relocation

  • Data relocation within the disk.(Seamless)
  • Data relocation by hardware.(By PV)
  • Software relocation by software.(By Device Driver)
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    Data Relocation Within The Disk
    This is least complicated operation for data relocation. If the system fails to carry out data I/O requests, then it anticipates data corruption. So data protection is carried out by moving data automatically within disk. No notifications are generated.

    Hard Data Relocation
    This is slightly more complex way of data relocation. The operation is initiated and instructed by
    Physical Volume. In this case data is moved from one Physical Partition to another reserved physical partition. So, data location changes from one PP A to another PP B. After the completion of data relocation, the device driver continues to refer to old location, PP A, but the LVM device driver. Bad block directory is maintained by LVM device driver. Also it maintains the translation table which maps the bad block PP A to good block PP B. Let’s say PP A location was bad block. So, it will be in the bad block directory of LVM device driver. Whenever some request comes for some I/O operation for any block, the device driver will look its bad block directory. If the block is listed in that, it translates the location requested to corresponding good location, say PP B, where the actual data is residing. Hence data protection is ensured in most cases.

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    One Response to “How Does AIX Deal With Bad Blocks”

    1. How To List Volume Groups and Their Characteristics | World is Welcome To The World of Unix!!! Says:

      […] BB Policy: Its bad block relocation policy. So, this value here is relocatable, that means we are allowed to relocate bad blocks in this Volume Group if need be. […]

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