Data scrubbing

 

Data scrubbing is an technique that uses a background task to periodically inspect or for errors, then correct detected errors using in the form of different checksums or copies of data. Data scrubbing reduces the likelihood that single correctable errors will accumulate, leading to reduced risks of uncorrectable errors.

is a high-priority concern in writing, reading, storage, transmission, or processing of the in computer and in computer storage and data transmission systems. However, only a few of the currently existing and used file systems provide sufficient protection against .

To address this issue, data scrubbing provides routine checks of all in data and, in general, prevention of hardware or software failure. This “scrubbing” feature occurs commonly in memory, disk arrays, , or as a mechanism of error detection and correction.

Contents

RAID

With data scrubbing, a RAID controller may periodically read all in a RAID array and check for defective blocks before applications might actually access them. This reduces the probability of silent data corruption and data loss due to bit-level errors.

In RAID environments, a feature called “patrol read” can perform data scrubbing and preventive maintenance.

, as a implementation, makes data consistency checks available and provides automated repairing of detected data inconsistencies. Such procedures are usually performed by setting up a weekly job. Maintenance is performed by issuing operations check, repair, or idle to each of the examined MD devices. Statuses of all performed operations, as well as general RAID statuses, are always available.

File systems

Btrfs

As a (CoW) for Linux, provides fault isolation, corruption detection and correction, and file-system scrubbing. If the file system detects a checksum mismatch while reading a block, it first tries to obtain (or create) a good copy of this block from another device if its internal mirroring or RAID techniques are in use.

Btrfs can initiate an online check of the entire file system by triggering a file system scrub job that is performed in the background. The scrub job scans the entire file system for integrity and automatically attempts to report and repair any bad blocks it finds along the way.

ZFS

The features of ZFS, which is a combined and , include the verification against modes, continuous integrity checking, and automatic repair. designed ZFS from the ground up with a focus on data integrity and to protect the data on disks against issues such as disk firmware bugs and .

ZFS provides a repair utility called <code>scrub</code> that examines and repairs silent caused by and other problems.

Memory

Due to the high integration density of contemporary computer memory , the individual memory cell structures became small enough to be vulnerable to and/or emission. The errors caused by these phenomena are called . This can be a problem for – and -based memories.

Memory scrubbing does error-detection and correction of bit errors in computer by using , other copies of the data, or other error-detecting codes.

FPGA

Scrubbing is a technique used to reprogram an . It can be used periodically to avoid the accumulation of errors without the need to find one in the configuration bitstream, thus simplifying the design.

Numerous approaches can be taken with respect to scrubbing, from simply reprogramming the FPGA to partial reconfiguration. The simplest method of scrubbing is to completely reprogram the FPGA at some periodic rate (typically 1/10 the calculated upset rate). However, the FPGA is not operational during that reprogram time, on the order of micro to milliseconds. For situations that cannot tolerate that type of interruption, partial reconfiguration is available. This technique allows the FPGA to be reprogrammed while still operational.

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Source

http://wikipedia.org/