You do not have permission to edit this page, for the following reasons:

This IP address has been blocked from editing Wikipedia.
This does not affect your ability to read Wikipedia pages.
Most people who see this message have done nothing wrong. Some kinds of blocks restrict editing from specific service providers or telecom companies in response to recent abuse or vandalism, and can sometimes affect other users who are unrelated to that abuse. Review the information below for assistance if you do not believe that you have done anything wrong.

The IP address or range 3.86.0.0/16 has been blocked (disabled) by ‪ST47‬ for the following reason(s):

The IP address that you are currently using has been blocked because it is believed to be a web host provider. To prevent abuse, web hosts may be blocked from editing Wikipedia.
You will not be able to edit Wikipedia using a web host provider because it hides your IP address, much like a proxy or VPN.
We recommend that you attempt to use another connection to edit. For example, if you use a proxy or VPN to connect to the internet, turn it off when editing Wikipedia. If you edit using a mobile connection, try using a Wi-Fi connection, and vice versa. If you are using a corporate internet connection, switch to a different Wi-Fi network. If you have a Wikipedia account, please log in.
If you do not have any other way to edit Wikipedia, you will need to request an IP block exemption.

How to appeal if you are confident that your connection does not use a web host's IP address:
If you are confident that you are not using a web host, you may appeal this block by adding the following text on your talk page: ((unblock|reason=Caught by a web host block but this host or IP is not a web host. My IP address is _______. Place any further information here. ~~~~)). You must fill in the blank with your IP address for this block to be investigated. Your IP address can be determined here. Alternatively, if you wish to keep your IP address private you can use the unblock ticket request system. There are several reasons you might be editing using the IP address of a web host (such as if you are using VPN software or a business network); please use this method of appeal only if you think your IP address is in fact not a web host.

Administrators: The IP block exemption user right should only be applied to allow users to edit using web host in exceptional circumstances, and they should usually be directed to the functionaries team via email. If you intend to give the IPBE user right, a CheckUser needs to take a look at the account. This can be requested most easily at SPI Quick Checkuser Requests. Unblocking an IP or IP range with this template is highly discouraged without at least contacting the blocking administrator.

This block will expire on 01:01, 24 April 2026.

Even when blocked, you will usually still be able to edit your user talk page, as well as email administrators and other editors.

For information on how to proceed, please read the FAQ for blocked users and the guideline on block appeals. The guide to appealing blocks may also be helpful.

Other useful links: Blocking policy · Help:I have been blocked
Your IP address is in a range that has been blocked on all Wikimedia Foundation wikis. The block was made by ‪Jon Kolbert‬. The reason given is Open proxy/Webhost: See the help page if you are affected .
- Start of block: 05:35, 21 February 2024
- Expiry of block: 05:35, 21 February 2029
Your current IP address is 3.86.82.155. The blocked range is 3.86.0.0/16. Please include all above details in any queries you make. If you believe you were blocked by mistake, you can find additional information and instructions in the No open proxies global policy. Otherwise, to discuss the block please post a request for review on Meta-Wiki. You could also send an email to the stewards VRT queue at stewards@wikimedia.org including all above details.

You can view and copy the source of this page:

((More citations needed|date=September 2013))
[[File:Raid1 Version for Wiki.jpg|thumb|RAID 1 layout]]

In [[Data storage device|data storage]], '''disk mirroring''' is the [[Replication (computing)|replication]] of [[logical disk]] volumes onto separate physical [[hard disk]]s in [[Real-time computing|real time]] to ensure [[continuous availability]]. It is most commonly used in [[RAID 1]]. A '''mirrored volume''' is a complete logical representation of separate volume copies.

In a [[disaster recovery]] context, mirroring data over long distance is referred to as [[storage replication]]. Depending on the technologies used, replication can be performed [[synchronous]]ly, [[Asynchronous communication|asynchronously]], semi-synchronously, or point-in-time. Replication is enabled via [[microcode]] on the [[disk array controller]] or via [[Server (computing)|server]] [[software]]. It is typically a proprietary solution, not compatible between various data storage device vendors.

Mirroring is typically only synchronous. Synchronous writing typically achieves a [[recovery point objective]] (RPO) of zero lost data. Asynchronous replication can achieve an RPO of just a few seconds while the remaining methodologies provide an RPO of a few minutes to perhaps several hours.

Disk mirroring differs from [[file shadowing]] that operates on the file level, and [[disk snapshot]]s where data images are never re-synced with their origins.

== Overview <span class="anchor" id="Resilvering"></span>==
Typically, mirroring is provided in either hardware solutions such as [[disk array]]s, or in software within the operating system (such as Linux [[mdadm]] and [[Device mapper#Features|device mapper]]).<ref>((cite web
 | url = http://article.gmane.org/gmane.linux.raid/44013
 | title = ANNOUNCE: mdadm 3.3 - A tools for managing md Soft RAID under Linux
 | date = 2013-09-03
 | access-date = 2013-11-20
 | website = gmane.org
 | archive-url = https://web.archive.org/web/20140821023250/http://article.gmane.org/gmane.linux.raid/44013
 | archive-date = 2014-08-21
 ))</ref><ref>((cite web
 | url = https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/device_mapper.html
 | title = Logical Volume Manager Administration
 | work = Appendix A. The Device Mapper
 | access-date = 2013-09-29
 | publisher = [[Red Hat]]
))</ref>  Additionally, [[file system]]s like [[Btrfs]] or [[ZFS]] provide integrated data mirroring.<ref>((cite web
 | url = https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices
 | title = Using Btrfs with Multiple Devices
 | date = 2013-11-07 | access-date = 2013-11-20
 | website = kernel.org
))</ref><ref>((cite web
 | url = http://www.c0t0d0s0.org/archives/7642-Actually-its-a-n-way-mirror.html
 | title = Actually it's a n-way mirror
 | date = 2013-09-04
 | access-date = 2013-11-20
 | website = c0t0d0s0.org
 | archive-date = 2013-09-14
 | archive-url = https://web.archive.org/web/20130914022916/http://www.c0t0d0s0.org/archives/7642-Actually-its-a-n-way-mirror.html
 ))</ref>  There are additional benefits from Btrfs and ZFS, which maintain both data and metadata integrity checksums, making themselves capable of detecting bad copies of blocks, and using mirrored data to pull up data from correct blocks.<ref>((cite web
 |url         = http://www.linuxfoundation.org/news-media/blogs/browse/2009/06/conversation-chris-mason-btrfs-next-generation-file-system-linux
 |archive-url  = https://web.archive.org/web/20120627065427/http://www.linuxfoundation.org/news-media/blogs/browse/2009/06/conversation-chris-mason-btrfs-next-generation-file-system-linux
 |archive-date = 27 June 2012
 |title       = A Conversation with Chris Mason on BTRfs: the next generation file system for Linux
 |first       = Amanda
 |last        = McPherson
 |date        = 22 June 2009
 |access-date  = 2013-11-22
 |publisher   = [[Linux Foundation]]
))</ref>

There are several scenarios for what happens when a disk fails. In a [[hot swap]] system, in the event of a disk failure, the system itself typically diagnoses a disk failure and signals a failure. Sophisticated systems may automatically activate a [[hot standby]] disk and use the remaining active disk to copy live data onto this disk. Alternatively, a new disk is installed and the data is copied to it. In less sophisticated systems, the system is operated on the remaining disk until a spare disk can be installed.

The copying of data from one side of a mirror pair to another is called ''rebuilding'' or, less commonly, ''resilvering''.<ref>((cite web |url=http://lonesysadmin.net/2012/03/23/why-is-it-called-resilvering/ |title=Why Is It Called 'Resilvering'? |website=The Lone SysAdmin |date=23 March 2012 |access-date=2013-09-19 ))</ref>

Mirroring can be performed site to site either by rapid data links, for example fibre optic links, which over distances of 500&nbsp;m or so can maintain adequate performance to support real-time mirroring. Longer distances or slower links maintain mirrors using an asynchronous copying system. For remote disaster recovery systems, this mirroring may not be done by integrated systems but simply by additional applications on primary and secondary machines.

== Additional benefits ==
In addition to providing an additional copy of the data for the purpose of redundancy in case of hardware failure, disk mirroring can allow each disk to be accessed separately for reading purposes. Under certain circumstances, this can significantly improve performance as the system can choose for each read which disk can seek most quickly to the required data. This is especially significant where there are several tasks competing for data on the same disk, and thrashing (where the switching between tasks takes up more time than the task itself) can be reduced. This is an important consideration in hardware configurations that frequently access the data on the disk.

== See also ==
* ((Annotated link|Business continuance volume))
* [[Disk cloning]]
* [[Distributed Replicated Block Device]] (DRBD)
* [[Mirror site]]
* [[Stable storage]]

== References ==
((Reflist))

((RAID))

[[Category:Fault-tolerant computer systems]]
[[Category:RAID]]

Pages transcluded onto the current version of this page (help):

Business continuance volume (edit)
Disk mirroring (edit)
Template:Ambox (view source) (template editor protected)
Template:Annotated link (view source) (template editor protected)
Template:Cite web (view source) (protected)
Template:Find sources mainspace (view source) (template editor protected)
Template:Hlist/styles.css (view source) (protected)
Template:Main other (view source) (protected)
Template:More citations needed (view source) (template editor protected)
Template:Navbox (view source) (template editor protected)
Template:RAID (edit)
Template:Reflist (view source) (protected)
Template:Reflist/styles.css (view source) (protected)
Module:Annotated link (view source) (template editor protected)
Module:Arguments (view source) (protected)
Module:Category handler (view source) (protected)
Module:Category handler/blacklist (view source) (protected)
Module:Category handler/config (view source) (protected)
Module:Category handler/data (view source) (protected)
Module:Category handler/shared (view source) (protected)
Module:Check for unknown parameters (view source) (protected)
Module:Citation/CS1 (view source) (protected)
Module:Citation/CS1/COinS (view source) (protected)
Module:Citation/CS1/Configuration (view source) (protected)
Module:Citation/CS1/Date validation (view source) (protected)
Module:Citation/CS1/Identifiers (view source) (protected)
Module:Citation/CS1/Utilities (view source) (protected)
Module:Citation/CS1/Whitelist (view source) (protected)
Module:Citation/CS1/styles.css (view source) (protected)
Module:Find sources (view source) (template editor protected)
Module:Find sources/config (view source) (template editor protected)
Module:Find sources/links (view source) (template editor protected)
Module:Find sources/templates/Find sources mainspace (view source) (template editor protected)
Module:GetShortDescription (view source) (template editor protected)
Module:Lang (view source) (template editor protected)
Module:Lang/ISO 639 synonyms (view source) (template editor protected)
Module:Lang/data (view source) (template editor protected)
Module:Language/data/iana languages (view source) (template editor protected)
Module:Language/data/iana regions (view source) (template editor protected)
Module:Language/data/iana scripts (view source) (template editor protected)
Module:Language/data/iana suppressed scripts (view source) (template editor protected)
Module:Language/data/iana variants (view source) (template editor protected)
Module:Message box (view source) (protected)
Module:Message box/ambox.css (view source) (protected)
Module:Message box/configuration (view source) (protected)
Module:Namespace detect/config (view source) (protected)
Module:Namespace detect/data (view source) (protected)
Module:Navbar (view source) (protected)
Module:Navbar/configuration (view source) (protected)
Module:Navbar/styles.css (view source) (protected)
Module:Navbox (view source) (template editor protected)
Module:Navbox/configuration (view source) (template editor protected)
Module:Navbox/styles.css (view source) (template editor protected)
Module:Unicode data (view source) (template editor protected)
Module:Unsubst (view source) (protected)
Module:Yesno (view source) (protected)

Return to Disk mirroring.

Retrieved from "https://en.wikipedia.org/wiki/Disk_mirroring"