Linux Raid

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("top of my head" summary of why fakeraid is bad... probably has errors/bias :))
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[ thesis writing]

Revision as of 11:52, 2 December 2010

This site is the Linux-raid kernel list community-managed reference for Linux software RAID as implemented in recent 2.6 kernels. It should replace many of the unmaintained and out-of-date documents out there such as the Software RAID HOWTO and the Linux RAID FAQ.

Where possible, information should be tagged with the minimum kernel/software version required to use the feature. Some of the information on these pages are unfortunately quite old, but we are in the process of updating the info (aren't we always...)

Linux RAID issues are discussed in the linux-raid mailing list to be found at


Help wanted

Please contact David Greaves or Nick Yeates if you'd like to help with this site.


There is an Overview section that is based on the RAID HowTo, covering the following:

The document is sprinkled with references to the deprecated raidtools which are being gradually removed.

Frequently Asked Questions - FAQ

Here goes a collection of frequently asked questions.

A mdadm-faq is available.

Areas Of Interest

Hardware RAID

Proper hardware RAID systems are presented to linux as a block device and there's no coverage of them (yet) in this wiki.

BIOS / firmware RAID aka fake raid cards:

  • offer no performance benefits and can often be slower than SW raid (link?)
  • if the 'raid' card or motherboard dies then you often have to find an exact replacement and this can be tricky for older cards
  • if drives move to other machines the data can't easily be read
  • there is usually no monitoring or reporting on the array - if a problem occurs then it may not show up unless the machine is rebooted *and* someone is actually watching the BIOS boot screen (or until multiple errors occur and your data is lost)
  • you are entrusting your data to unpatchable software written into a BIOS that has probably not been tested, has no support mechanism and almost no community.
  • having seen how many bugs the kernel works around in various BIOSes it would be optimistic to think that the BIOS RAID has no bugs.

Given the point of RAID is usually to reduce risk it's fair to say that using fakeraid is a terrible idea and it's better to focus energy on either true HW raid or in-kernel SW raid .... but there's nothing stopping you :)

External links

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thesis writing

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