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Load the log from each disk when starting the array and recover if the array is dirty. The initial empty PPL is written by mdadm. When loading the log we verify the header checksum and signature. For external metadata arrays the signature is verified in userspace, so here we read it from the header, verifying only if it matches on all disks, and use it later when writing PPL. In addition to the header checksum, each header entry also contains a checksum of its partial parity data. If the header is valid, recovery is performed for each entry until an invalid entry is found. If the array is not degraded and recovery using PPL fully succeeds, there is no need to resync the array because data and parity will be consistent, so in this case resync will be disabled. Due to compatibility with IMSM implementations on other systems, we can't assume that the recovery data block size is always 4K. Writes generated by MD raid5 don't have this issue, but when recovering PPL written in other environments it is possible to have entries with 512-byte sector granularity. The recovery code takes this into account and also the logical sector size of the underlying drives. Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com> Signed-off-by: Shaohua Li <shli@fb.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.