geom_raid5 is a storage module created for the

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operating system. It facilitates

RAID5 In computer storage, the standard RAID levels comprise a basic set of RAID ("redundant array of independent disks" or "redundant array of inexpensive disks") configurations that employ the techniques of striping, mirroring, or parity to create larg ...

functionality without the need of a hardware RAID controller. geom_raid5 allows storage of large amounts of data to be protected against disk failure, while providing good throughput performance. Like other FreeBSD storage modules, geom_raid5 utilizes the

GEOM GEOM is the main storage framework for the FreeBSD operating system. It is available in FreeBSD 5.0 and later releases, and provides a standardized way to access storage layers. GEOM is modular and allows for ''geom modules'' to connect to the fra ...

framework. It is built as a kernel loadable module (KLD) which allows it to run inside the FreeBSD kernel. The module can be compiled on FreeBSD release 5 and newer releases. geom_raid5 is also incorporated into

FreeNAS TrueNAS is the branding for a range of free and open-source network-attached storage (NAS) operating systems produced by iXsystems, and based on FreeBSD and Linux, using the OpenZFS file system. It is licensed under the terms of the BSD Li ...

, an operating system dedicated to

Network Attached Storage Network-attached storage (NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the techn ...

. Its author, Arne Woerner, has released the software under the BSD license, making geom_raid5

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-compliant

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software.

Comparing to other Software RAID5 solutions

geom_raid5 distinguishes itself by providing both advanced features and high performance. While the theoretical maximum write speed is , the latest version is able to achieve about 80% of that theoretical maximum. This is in huge contrast with other software RAID5 solutions{{Citation needed, date=May 2008 which sometimes achieve less than 10% of that throughput combined with significantly higher

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

utilization. The reason for this huge difference lies in geom_raid5's design. In order to write data to a RAID5 volume, data must often first be read in order to calculate the parity information that protects against data loss in case of a single disk failure. Using request combining a full stripe block can be 'collected' so a read is no longer required. This means the harddrive heads do not need to change position every time but can write data contiguously, theoretically at full speed. Of course, this only works with sequential transfers and sometimes even then the filesystem does not write contiguously. But using request combining, geom_raid5 manages to outperform any software RAID5 solution to date, capable of reaching write-speeds associated with hardware RAID5 on budget-level

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hardware. Currently the module is being finalized. When a stable version is released the author will release further information about its design and disclose benchmarks. In particular, benchmarks showing geom_raid5 performance versus

ZFS ZFS (previously: Zettabyte File System) is a file system with volume management capabilities. It began as part of the Sun Microsystems Solaris operating system in 2001. Large parts of Solaris – including ZFS – were published under an open ...

RAID-Z Although all RAID implementations differ from the specification to some extent, some companies and open-source projects have developed non-standard RAID implementations that differ substantially from the standard. Additionally, there are non-RAID ...

are long-awaited by users.

Variants

Various incarnations of geom raid5 exist which trade off speed for memory usage. * geom_raid5 The most stable version but slower than the other variants in certain cases * geom_raid5 TNG Uses more memory to deliver better transfer rates * geom_raid5 PP Memory usage and speed is in between the TNG and PP. Uses less memory than TNG but is slower. Uses more memory than the original geom_raid5 driver and is faster. It is also claimed that PP's code best being the cleanest of the three

External links

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repository for geom_raid5
* geom_raid5 sources: http://www.wgboome.org/geom_raid5.html RAID FreeBSD