Data scrubbing

Data scrubbing is an error correction technique that uses a background task to periodically inspect main memory or storage for errors, then correct detected errors using redundant data 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. Data scrubbing is an error correction technique that uses a background task to periodically inspect main memory or storage for errors, then correct detected errors using redundant data 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. Data integrity is a high-priority concern in writing, reading, storage, transmission, or processing of the computer data in computer operating systems and in computer storage and data transmission systems. However, only a few of the currently existing and used file systems 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, file systems, or FPGAs as a mechanism of error detection and correction. With data scrubbing, a RAID controller may periodically read all hard disk drives 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 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.