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authorBoaz Harrosh <bharrosh@panasas.com>2011-10-14 15:33:51 +0200
committerBoaz Harrosh <bharrosh@panasas.com>2011-10-24 17:15:33 -0700
commit769ba8d92025fa390f3097e658b8ed6e032d68e9 (patch)
treeeec1a556d6b3796f702c96e7f97ce94ba7d9d410 /fs/exofs/Kconfig
parenta1fec1dbbc8db974d2582e4040590cebe72171e4 (diff)
ore: RAID5 Write
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>
Diffstat (limited to 'fs/exofs/Kconfig')
-rw-r--r--fs/exofs/Kconfig9
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/exofs/Kconfig b/fs/exofs/Kconfig
index 70bae414929..fa9a286c877 100644
--- a/fs/exofs/Kconfig
+++ b/fs/exofs/Kconfig
@@ -1,10 +1,17 @@
+# Note ORE needs to "select ASYNC_XOR". So Not to force multiple selects
+# for every ORE user we do it like this. Any user should add itself here
+# at the "depends on EXOFS_FS || ..." with an ||. The dependencies are
+# selected here, and we default to "ON". So in effect it is like been
+# selected by any of the users.
config ORE
tristate
+ depends on EXOFS_FS
+ select ASYNC_XOR
+ default SCSI_OSD_ULD
config EXOFS_FS
tristate "exofs: OSD based file system support"
depends on SCSI_OSD_ULD
- select ORE
help
EXOFS is a file system that uses an OSD storage device,
as its backing storage.