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Dell PowerVault ME4 Series Storage System CLI Guide

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show fenced-data


Description	Shows information about fenced data blocks in the storage system. The command will show information for all fenced blocks by default, or you can use parameters to filter the output. Fenced data blocks are blocks of data on disk which, for either of the following reasons, cannot be recovered and have been lost: 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. # show fenced-data all
Basetypes	fenced-data status
See also	show disk-groups show events show vdisks show volumes