(I already posted this to LKML a few hours ago but forgot to post it over here)
All,
Adaptec has been looking at the MD driver for a foundation for their Open-Source software RAID stack. This will help us provide full and open support for current and future Adaptec RAID products (as opposed to the limited support through closed drivers that we have now).
While MD is fairly functional and clean, there are a number of enhancements to it that we have been working on for a while and would
like to push out to the community for review and integration. These
include:
- partition support for md devices: MD does not support the concept of fdisk partitions; the only way to approximate this right now is by creating multiple arrays on the same media. Fixing this is required for not only feature-completeness, but to allow our BIOS to recognise the partitions on an array and properly boot them as it would boot a normal disk.
- generic device arrival notification mechanism: This is needed to support device hot-plug, and allow arrays to be automatically configured regardless of when the md module is loaded or initialized. RedHat EL3 has a scaled down version of this already, but it is specific to MD and only works if MD is statically compiled into the kernel. A general mechanism will benefit MD as well as any other storage system that wants hot-arrival notices.
- RAID-0 fixes: The MD RAID-0 personality is unable to perform I/O that spans a chunk boundary. Modifications are needed so that it can take a request and break it up into 1 or more per-disk requests.
- Metadata abstraction: We intend to support multiple on-disk metadata formats, along with the 'native MD' format. To do this, specific knowledge of MD on-disk structures must be abstracted out of the core and personalities modules.
- DDF Metadata support: Future products will use the 'DDF' on-disk metadata scheme. These products will be bootable by the BIOS, but must have DDF support in the OS. This will plug into the abstraction mentioned above.
I'm going to push these changes out in phases in order to keep the risk and churn to a minimum. The attached patch is for the partition support. It was originally from Ingo Molnar, but has changed quite a bit due to the radical changes in the disk/block layer in 2.6. The 2.4 version works quite well, while the 2.6 version is fairly fresh. One problem that I have with it is that the created partitions show up in /proc/partitions after running fdisk, but not after a reboot.
Scott
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