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Storage

The developers have extracted the MD subsystem's RAID-6 code to enable the Btrfs file system to use this code. In 2.6.36, the MD subsystem's RAID-5 code will offer various entry points that allow Device Mapper targets to use the RAID-5 infrastructure (1, 2) – however, the Device Mapper code required for this functionality has not been included in this development cycle. In the long run, the code is to enable the dmraid userspace program to provide the HostRAID-5 functions offered by many modern motherboard chip-sets and RAID adapters; this currently requires various extensions which have long been maintained outside of the main Linux development branch.

The developers have extended the linear, delay, stripe and mpath Device Mapper targets to include discard support – if the file system and storage hardware also support the discard target, the kernel can inform storage devices accessed via the Device Mapper about newly available storage areas, which can improve the performance and life span of SSDs. The SCSI subsystem, which offers basic functions for ATA and Fibre Channel hardware, now also includes the infrastructure required for accessing the run-time power saving features offered by I / O devices. However, none of the PCI / PCIe drivers in this subsystem uses these features yet.

About the source code management system

Many of the links in this article point to the relevant commits in the web front end of Linus Torvalds' Git source code management system for Linux, because these commits tend to contain a lot more information about the respective changes. The commit comment in the mid section of the web page displayed by the Git web front end is often a particularly helpful source of further information. This is where the author of a patch usually describes the background and intended effects of the changes.

The bottom section of the Git web front end lists the files that are affected by the patch. The "diff" link behind each file name shows how the patch modifies the respective file; if you want to view the complete patch in its raw form, click on the commitdiff link. Even if you don't have any programming skills the patches are often a good source of information, because they also contain changes to the documentation and comments within the code.

Networking

Due to SR-IOV, the new cxgb4vf driver for guest systems can now directly access some of the features offered by Chelsio's 1-Gigabit and 10-Gigabit network chips; as with other SR-IOV drivers, this is designed to reduce latencies and CPU loads for network transfers and increase data throughput (for instance 1, 2, 3, 4, 5). The Atheros ath9k Wi-Fi driver can now talk to version 2.2 of the AR9003 chip. The Minstrel rate control algorithm, which originated from the MadWifi project and automatically selects the most suitable transmission method, now supports 802.11n transmissions. The ipheth iPhone tethering driver can now interact with the iPhone 4.

Next: Architecture code, Memory subsystem & Security

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