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Some details of the chkdosfs utility

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Applicable Environment

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Topic: chkdosfs utility
SDP: 6.4.0
Target: Any supported target

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Recommendation

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chkdosfs runs in four phases:

Phase 1:

1. check for invalid media byte
Type: Metadata
Action: error is recoverable. No data loss.
2. Reserved FAT entries incorrectly marked
Type Metadata
Action: error is recoverable. No data loss.
3. Cluster validation
Type: Metadata and user data
Action: error is recoverable. Data loss is unlikely.

Phase 2:

1. Clear Chain/Truncate verification
Type: Metadata and user data
Action: data is unrecoverable
2. Cluster chain ending out of range
Type: Metadata and user data
Action: data is unrecoverable
3. Cluster contains a cycle
Type: Metadata and user data
Action: data is unrecoverable
4. Last cluster is un-readable
Type: Metadata and user data
Action: None, display warning

Phase 3: Check Directories

1. Root directory starts with a cluster our of range
Type: User data
Action: Fatal error, root directory unrecoverable
2. Root directory starts with a free cluster
Type: User data
Action: Recoverable
3. Root directory doesn't start with a cluster chain
Type: User data
Action: Fatal error, root directory unrecoverable

Phase 4: Check for lost files

1. Lost cluster chain
Type: User and meta data
Action: Clear the chain, data will be lost if recovery attempt fails

In short you will lose files/directories when the entire cluster chain is not completely committed to the storage medium. Most errors are recoverable however expect not to be able to recover files if any portion of them is missing.

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NOTE: This entry has been validated against the SDP version listed above. Use caution when considering this advice for any other SDP version. For supported releases, please reach out to QNX Technical Support if you have any questions/concerns.

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