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path: root/fs/exofs/ore_raid.h
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2011-10-24ore: RAID5 WriteBoaz Harrosh
This is finally the RAID5 Write support. The bigger part of this patch is not the XOR engine itself, But the read4write logic, which is a complete mini prepare_for_striping reading engine that can read scattered pages of a stripe into cache so it can be used for XOR calculation. That is, if the write was not stripe aligned. The main algorithm behind the XOR engine is the 2 dimensional array: struct __stripe_pages_2d. A drawing might save 1000 words --- __stripe_pages_2d | n = pages_in_stripe_unit; w = group_width - parity; | pages array presented to the XOR lib | | V | __1_page_stripe[0].pages --> [c0][c1]..[cw][c_par] <---| | | __1_page_stripe[1].pages --> [c0][c1]..[cw][c_par] <--- | ... | ... | __1_page_stripe[n].pages --> [c0][c1]..[cw][c_par] ^ | data added columns first then row --- The pages are put on this array columns first. .i.e: p0-of-c0, p1-of-c0, ... pn-of-c0, p0-of-c1, ... So we are doing a corner turn of the pages. Note that pages will zigzag down and left. but are put sequentially in growing order. So when the time comes to XOR the stripe, only the beginning and end of the array need be checked. We scan the array and any NULL spot will be field by pages-to-be-read. The FS that wants to support RAID5 needs to supply an operations-vector that searches a given page in cache, and specifies if the page is uptodate or need reading. All these pages to be read are put on a slave ore_io_state and synchronously read. All the pages of a stripe are read in one IO, using the scatter gather mechanism. In write we constrain our IO to only be incomplete on a single stripe. Meaning either the complete IO is within a single stripe so we might have pages to read from both beginning or end of the strip. Or we have some reading to do at beginning but end at strip boundary. The left over pages are pushed to the next IO by the API already established by previous work, where an IO offset/length combination presented to the ORE might get the length truncated and the user must re-submit the leftover pages. (Both exofs and NFS support this) But any ORE user should make it's best effort to align it's IO before hand and avoid complications. A cached ore_layout->stripe_size member can be used for that calculation. (NOTE: that ORE demands that stripe_size may not be bigger then 32bit) What else? Well read it and tell me. Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
2011-10-24ore: RAID5 readBoaz Harrosh
This patch introduces the first stage of RAID5 support mainly the skip-over-raid-units when reading. For writes it inserts BLANK units, into where XOR blocks should be calculated and written to. It introduces the new "general raid maths", and the main additional parameters and components needed for raid5. Since at this stage it could corrupt future version that actually do support raid5. The enablement of raid5 mounting and setting of parity-count > 0 is disabled. So the raid5 code will never be used. Mounting of raid5 is only enabled later once the basic XOR write is also in. But if the patch "enable RAID5" is applied this code has been tested to be able to properly read raid5 volumes and is according to standard. Also it has been tested that the new maths still properly supports RAID0 and grouping code just as before. (BTW: I have found more bugs in the pnfs-obj RAID math fixed here) The ore.c file is getting too big, so new ore_raid.[hc] files are added that will include the special raid stuff that are not used in striping and mirrors. In future write support these will get bigger. When adding the ore_raid.c to Kbuild file I was forced to rename ore.ko to libore.ko. Is it possible to keep source file, say ore.c and module file ore.ko the same even if there are multiple files inside ore.ko? Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>