Geom raid5
Encyclopedia
geom_raid5 is a storage module created for the FreeBSD
operating system. It facilitates RAID5 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
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
, an Operating System dedicated to Network Attached Storage
. Its author, Arne Woerner, has released the software under the BSD license, making geom_raid5 OSI
-compliant open source
software.
· ( - 1) , the latest version is able to achieve about 80% of that theoretical maximum. This is in huge contrast with other software RAID5 solutions which sometimes achieve less than 10% of that throughput combined with significantly higher CPU 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 x86 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
's RAID-Z are long awaited by users.
The most stable version but slower than the other variants in certain cases
Uses more memory to deliver better transfer rates
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
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
operating system. It facilitates RAID5 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
GEOM is the main storage framework for the FreeBSD operating system. It is available in FreeBSD 5.0 and higher and provides a standardized way to access storage layers. GEOM is modular and allows for geom modules to connect to the framework. For example, the geom_mirror module will provide RAID1 or...
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
FreeNAS
FreeNAS is a free network-attached storage server, supporting: CIFS , FTP, NFS, rsync, AFP protocols, iSCSI, S.M.A.R.T., local user authentication, and software RAID , with a web-based configuration interface. FreeNAS takes less than 64 MB once installed on CompactFlash, hard drive or USB flash...
, an Operating System dedicated to Network Attached Storage
Nas
Nasir bin Olu Dara Jones, who performs under the name Nas , formerly Nasty Nas, is an American rapper and actor. He is regarded as one of the most important figures in hip hop and one of the most skilled and influential rappers of all-time...
. Its author, Arne Woerner, has released the software under the BSD license, making geom_raid5 OSI
Open Source Initiative
The Open Source Initiative is an organization dedicated to promoting open source software.The organization was founded in February 1998, by Bruce Perens and Eric S. Raymond, prompted by Netscape Communications Corporation publishing the source code for its flagship Netscape Communicator product...
-compliant open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
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 isThe 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 x86 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
In computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
's RAID-Z 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
- FreeBSDFreeBSDFreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
perforcePerforcePerforce is a commercial, proprietary, centralized revision control system developed by Perforce Software, Inc.-Architecture:Perforce is a client/server system.The server manages a central database and a master repository of file versions....
: repository for geom_raid5 - geom_raid5 sources: http://www.wgboome.org/geom_raid5.html