Support multiple physical spindles through a single logical device. Required for RAID and logical volume management.
This driver lets you combine several hard disk partitions into one logical block device. This can be used to simply append one partition to another one or to combine several redundant hard disks into a RAID1/4/5 device so as to provide protection against hard disk failures. This is called "Software RAID" since the combining of the partitions is done by the kernel. "Hardware RAID" means that the combining is done by a dedicated controller; if you have such a controller, you do not need to say Y here. More information about Software RAID on Linux is contained in the Software RAID mini-HOWTO, available from <http://www.tldp.org/docs.html#howto>. There you will also learn where to get the supporting user space utilities raidtools. If unsure, say N.
If you say Y here, then the kernel will try to autodetect raid arrays as part of its boot process. If you don't use raid and say Y, this autodetection can cause a several-second delay in the boot time due to various synchronisation steps that are part of this step. If unsure, say Y.
If you say Y here, then your multiple devices driver will be able to use the so-called linear mode, i.e. it will combine the hard disk partitions by simply appending one to the other. To compile this as a module, choose M here: the module will be called linear. If unsure, say Y.
If you say Y here, then your multiple devices driver will be able to use the so-called raid0 mode, i.e. it will combine the hard disk partitions into one logical device in such a fashion as to fill them up evenly, one chunk here and one chunk there. This will increase the throughput rate if the partitions reside on distinct disks. Information about Software RAID on Linux is contained in the Software-RAID mini-HOWTO, available from <http://www.tldp.org/docs.html#howto>. There you will also learn where to get the supporting user space utilities raidtools. To compile this as a module, choose M here: the module will be called raid0. If unsure, say Y.
A RAID-1 set consists of several disk drives which are exact copies of each other. In the event of a mirror failure, the RAID driver will continue to use the operational mirrors in the set, providing an error free MD (multiple device) to the higher levels of the kernel. In a set with N drives, the available space is the capacity of a single drive, and the set protects against a failure of (N - 1) drives. Information about Software RAID on Linux is contained in the Software-RAID mini-HOWTO, available from <http://www.tldp.org/docs.html#howto>. There you will also learn where to get the supporting user space utilities raidtools. If you want to use such a RAID-1 set, say Y. To compile this code as a module, choose M here: the module will be called raid1. If unsure, say Y.
RAID-10 provides a combination of striping (RAID-0) and mirroring (RAID-1) with easier configuration and more flexible layout. Unlike RAID-0, but like RAID-1, RAID-10 requires all devices to be the same size (or at least, only as much as the smallest device will be used). RAID-10 provides a variety of layouts that provide different levels of redundancy and performance. RAID-10 requires mdadm-1.7.0 or later, available at: ftp://ftp.kernel.org/pub/linux/utils/raid/mdadm/ If unsure, say Y.
A RAID-5 set of N drives with a capacity of C MB per drive provides the capacity of C * (N - 1) MB, and protects against a failure of a single drive. For a given sector (row) number, (N - 1) drives contain data sectors, and one drive contains the parity protection. For a RAID-4 set, the parity blocks are present on a single drive, while a RAID-5 set distributes the parity across the drives in one of the available parity distribution methods. A RAID-6 set of N drives with a capacity of C MB per drive provides the capacity of C * (N - 2) MB, and protects against a failure of any two drives. For a given sector (row) number, (N - 2) drives contain data sectors, and two drives contains two independent redundancy syndromes. Like RAID-5, RAID-6 distributes the syndromes across the drives in one of the available parity distribution methods. Information about Software RAID on Linux is contained in the Software-RAID mini-HOWTO, available from <http://www.tldp.org/docs.html#howto>. There you will also learn where to get the supporting user space utilities raidtools. If you want to use such a RAID-4/RAID-5/RAID-6 set, say Y. To compile this code as a module, choose M here: the module will be called raid456. If unsure, say Y.
Enable the raid456 module to dispatch per-stripe raid operations to a thread pool. If unsure, say N.
MD_MULTIPATH provides a simple multi-path personality for use the MD framework. It is not under active development. New projects should consider using DM_MULTIPATH which has more features and more testing. If unsure, say N.
The "faulty" module allows for a block device that occasionally returns read or write errors. It is useful for testing. In unsure, say N.
Device-mapper is a low level volume manager. It works by allowing people to specify mappings for ranges of logical sectors. Various mapping types are available, in addition people may write their own modules containing custom mappings if they wish. Higher level volume managers such as LVM2 use this driver. To compile this as a module, choose M here: the module will be called dm-mod. If unsure, say N.
Enable this for messages that may help debug device-mapper problems. If unsure, say N.
This device-mapper target allows you to create a device that transparently encrypts the data on it. You'll need to activate the ciphers you're going to use in the cryptoapi configuration. Information on how to use dm-crypt can be found on <http://www.saout.de/misc/dm-crypt/> To compile this code as a module, choose M here: the module will be called dm-crypt. If unsure, say N.
Allow volume managers to take writable snapshots of a device.
Allow volume managers to mirror logical volumes, also needed for live data migration tools such as 'pvmove'.
A dm target that supports RAID4, RAID5 and RAID6 mappings A RAID-5 set of N drives with a capacity of C MB per drive provides the capacity of C * (N - 1) MB, and protects against a failure of a single drive. For a given sector (row) number, (N - 1) drives contain data sectors, and one drive contains the parity protection. For a RAID-4 set, the parity blocks are present on a single drive, while a RAID-5 set distributes the parity across the drives in one of the available parity distribution methods. A RAID-6 set of N drives with a capacity of C MB per drive provides the capacity of C * (N - 2) MB, and protects against a failure of any two drives. For a given sector (row) number, (N - 2) drives contain data sectors, and two drives contains two independent redundancy syndromes. Like RAID-5, RAID-6 distributes the syndromes across the drives in one of the available parity distribution methods.
The userspace logging module provides a mechanism for relaying the dm-dirty-log API to userspace. Log designs which are more suited to userspace implementation (e.g. shared storage logs) or experimental logs can be implemented by leveraging this framework.
A target that discards writes, and returns all zeroes for reads. Useful in some recovery situations.
Allow volume managers to support multipath hardware.
This path selector is a dynamic load balancer which selects the path with the least number of in-flight I/Os. If unsure, say N.
This path selector is a dynamic load balancer which selects the path expected to complete the incoming I/O in the shortest time. If unsure, say N.
A target that delays reads and/or writes and can send them to different devices. Useful for testing. If unsure, say N.
Generate udev events for DM events.
A target that intermittently fails I/O for debugging purposes.