On Wed, Mar 07, 2018 at 12:08:09PM -0700, Liu Bo wrote: > 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....@oracle.com> > --- > v2: - Place bio allocation in code statement. > - Get rid of bio_set_op_attrs. > - Add SOB.
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