From f6bed0ef0a808164f51197de062e0450ce6c1f96 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Thu, 13 Aug 2015 14:31:59 -0700 Subject: raid5: add basic stripe log This introduces a simple log for raid5. Data/parity writing to raid array first writes to the log, then write to raid array disks. If crash happens, we can recovery data from the log. This can speed up raid resync and fix write hole issue. The log structure is pretty simple. Data/meta data is stored in block unit, which is 4k generally. It has only one type of meta data block. The meta data block can track 3 types of data, stripe data, stripe parity and flush block. MD superblock will point to the last valid meta data block. Each meta data block has checksum/seq number, so recovery can scan the log correctly. We store a checksum of stripe data/parity to the metadata block, so meta data and stripe data/parity can be written to log disk together. otherwise, meta data write must wait till stripe data/parity is finished. For stripe data, meta data block will record stripe data sector and size. Currently the size is always 4k. This meta data record can be made simpler if we just fix write hole (eg, we can record data of a stripe's different disks together), but this format can be extended to support caching in the future, which must record data address/size. For stripe parity, meta data block will record stripe sector. It's size should be 4k (for raid5) or 8k (for raid6). We always store p parity first. This format should work for caching too. flush block indicates a stripe is in raid array disks. Fixing write hole doesn't need this type of meta data, it's for caching extension. Signed-off-by: Shaohua Li Signed-off-by: NeilBrown --- drivers/md/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/md/Makefile') diff --git a/drivers/md/Makefile b/drivers/md/Makefile index 462f443a4f85..f34979cd141a 100644 --- a/drivers/md/Makefile +++ b/drivers/md/Makefile @@ -17,7 +17,7 @@ dm-cache-smq-y += dm-cache-policy-smq.o dm-cache-cleaner-y += dm-cache-policy-cleaner.o dm-era-y += dm-era-target.o md-mod-y += md.o bitmap.o -raid456-y += raid5.o +raid456-y += raid5.o raid5-cache.o # Note: link order is important. All raid personalities # and must come before md.o, as they each initialise -- cgit v1.2.3