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Data scrubbing is an error correction technique that uses a background task to periodically inspect main memory or storage for errors, then corrects detected errors using Data redundancy in the form of different or copies of data. Data scrubbing reduces the likelihood that single correctable errors will accumulate, leading to reduced risks of uncorrectable errors.
Data integrity is a high-priority concern in writing, reading, storage, transmission, or processing of data in computer and in computer storage and data transmission systems. However, only a few of the currently existing and used provide sufficient protection against data corruption.
To address this issue, data scrubbing provides routine checks of all inconsistencies in data and, in general, prevention of hardware or software failure. This "scrubbing" feature occurs commonly in memory, disk arrays, , or FPGAs as a mechanism of error detection and correction.
In Dell PowerEdge RAID environments, a feature called "patrol read" can perform data scrubbing and preventive maintenance.
In OpenBSD, the [[bioctl]](8) utility allows the system administrator to control these patrol reads through the BIOCPATROL ioctl on the /dev/bio pseudo-device; as of 2019, this functionality is supported in some device drivers for LSI Logic and Dell controllers — this includes mfi(4) since OpenBSD 5.8 (2015) and mfii(4) since OpenBSD 6.4 (2018).
In FreeBSD and DragonFly BSD, patrol can be controlled through a RAID controller-specific utility mfiutil(8) since FreeBSD 8.0 (2009) and 7.3 (2010).
The implementation from FreeBSD was used by the OpenBSD developers for adding patrol support to their generic bio(4) framework and the bioctl utility, without a need for a separate controller-specific utility.
In NetBSD in 2008, the bio(4) framework from OpenBSD was extended to feature support for consistency checks, which was implemented for /dev/bio pseudo-device under BIOCSETSTATE ioctl command, with the options being start and stop (BIOC_SSCHECKSTART_VOL and BIOC_SSCHECKSTOP_VOL, respectively); this is supported only by a single driver as of 2019 — arcmsr(4).
Linux MD RAID, as a software RAID implementation, makes data consistency checks available and provides automated repairing of detected data inconsistencies. Such procedures are usually performed by setting up a weekly cron 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.
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 provides a repair utility called scrub that examines and repairs silent data corruption caused by data degradation and other problems.
Memory scrubbing does error-detection and correction of bit errors in computer RAM by using ECC memory, other copies of the data, or other error-correction codes.
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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