Editing RAID (section)

== Non-standard levels ==
{{Main|Non-standard RAID levels}}

Many configurations other than the basic numbered RAID levels are possible, and many companies, organizations, and groups have created their own non-standard configurations, in many cases designed to meet the specialized needs of a small niche group. Such configurations include the following:

* [[Linux MD RAID 10]] provides a general RAID driver that in its "near" layout defaults to a standard RAID&nbsp;1 with two drives, and a standard RAID&nbsp;1+0 with four drives; however, it can include any number of drives, including odd numbers. With its "far" layout, MD RAID&nbsp;10 can run both striped and mirrored, even with only two drives in <code>f2</code> layout; this runs mirroring with striped reads, giving the read performance of RAID&nbsp;0. Regular RAID&nbsp;1, as provided by [[Linux software RAID]], does not stripe reads, but can perform reads in parallel.<ref name="layton-lm" /><ref>{{cite web |title=Performance, Tools & General Bone-Headed Questions |url=http://www.tldp.org/HOWTO/Software-RAID-0.4x-HOWTO-8.html |publisher=tldp.org |access-date=2013-12-25}}</ref><ref>{{cite web |title=Main Page – Linux-raid |url=http://linux-raid.osdl.org/ |publisher=osdl.org |date=2010-08-20 |access-date=2010-08-24 |url-status=dead |archive-url=https://web.archive.org/web/20080705104645/http://linux-raid.osdl.org/ |archive-date=2008-07-05 }}</ref>
* [[Hadoop]] has a RAID system that generates a parity file by xor-ing a stripe of blocks in a single HDFS file.<ref>{{cite web|url=http://hadoopblog.blogspot.com/2009/08/hdfs-and-erasure-codes-hdfs-raid.html |title=Hdfs Raid |publisher=Hadoopblog.blogspot.com |date=2009-08-28 |access-date=2010-08-24}}</ref>
* [[BeeGFS]], the parallel file system, has internal striping (comparable to file-based RAID0) and replication (comparable to file-based RAID10) options to aggregate throughput and capacity of multiple servers and is typically based on top of an underlying RAID to make disk failures transparent.
* [[Non-standard RAID levels#Declustered RAID|Declustered RAID]] scatters dual (or more) copies of the data across all disks (possibly hundreds) in a storage subsystem, while holding back enough spare capacity to allow for a few disks to fail. The scattering is based on algorithms which give the appearance of arbitrariness. When one or more disks fail the missing copies are rebuilt into that spare capacity, again arbitrarily. Because the rebuild is done from and to all the remaining disks, it operates much faster than with traditional RAID, reducing the overall impact on clients of the storage system.