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In case of raid56, writes and rebuilds always take BTRFS_STRIPE_LEN(64K)
as unit, however, scrub_extent() sets blocksize as unit, so rebuild
process may be triggered on every block on a same stripe.
A typical example would be that when we're replacing a disappeared disk,
all reads on the disks get -EIO, every block (size is 4K if blocksize is
4K) would go thru these,
scrub_handle_errored_block
scrub_recheck_block # re-read pages one by one
scrub_recheck_block # rebuild by calling raid56_parity_recover()
page by page
Although with raid56 stripe cache most of reads during rebuild can be
avoided, the parity recover calculation(xor or raid6 algorithms) needs to
be done $(BTRFS_STRIPE_LEN / blocksize) times.
This makes it smarter by doing raid56 scrub/replace on stripe length.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.