CLI Guide

• Typically, fenced data occurs when a disk in a non-fault-tolerant disk group detects an unrecoverable
media error.
• Fenced data can also occur if multiple unrecoverable blocks are detected which exceed the capacity of
the RAID error-recovery algorithms.
Unrecoverable data blocks are “fenced” by marking them unreadable by the storage system. A data block
remains fenced until the host writes the block, at which time it is again accessible.
For NRAID and RAID 0, fenced data is not tracked. Errors are returned directly during host reads.
For RAID 1 and 10, fenced blocks correspond with the data blocks where unrecoverable errors are detected,
normally when a disk group is not fault tolerant and the remaining good disk has a media error.
For RAID 3, 5, 6, 50 for linear storage or 5, 6, and ADAPT for virtual storage, a single unrecoverable error
detected while not fault tolerant can result in two or more blocks being fenced. This is because each parity
block protects multiple data blocks. Thus, for RAID 3, 5, and 50, if a block returns an unrecovered error
during reconstruction, that block is lost (because it cannot be read). The block being reconstructed is also
lost because there is not enough information to reconstruct the data for that block. RAID 6 and ADAPT will
similarly mark multiple bad blocks if a combination of failed disks and media errors results in unrecoverable
data.
When the controller module fences data, it logs events 542 and 543.
Minimum role monitor
Syntax
show fenced-data [all]
[disk-groups disk-groups]
[vdisks vdisks]
[volumes volumes]
Parameters
all
Optional. Shows information about all fenced data blocks.
[disk-groups disk-groups]
Optional. The names or serial numbers of disk groups for which to show fenced data block information. A
name that includes a space must be enclosed in double quotes.
[vdisks vdisks]
Optional. The names or serial numbers of disk groups for which to show fenced data block information. A
name that includes a space must be enclosed in double quotes.
[volumes volumes]
Optional for linear storage. The names or serial numbers of linear volumes for which to show fenced data
block information. A name that includes a space must be enclosed in double quotes.
Output
Volume Name
The volume name for which fenced data is reported.
Volume Serial Number
The volume serial number for which fenced data is reported.
Volume LBA
The LBA in the volume at which fenced data is reported.
Vdisk Name
The name of the disk group for which fenced data is reported.
Vdisk Serial Number
The serial number of the disk group for which fenced data is reported.
Vdisk LBA
The LBA in the disk group at which fenced data is reported.
Examples Show information about fenced data blocks for all volumes.
Alphabetical list of commands 199