kernel/linux.git/Documentation/admin-guide/md.rst, branch v6.19.11

md: allow configuring logical block size

2025-11-11T03:20:15+00:00

Previously, raid array used the maximum logical block size (LBS) of all member disks. Adding a larger LBS disk at runtime could unexpectedly increase RAID's LBS, risking corruption of existing partitions. This can be reproduced by: ``` # LBS of sd[de] is 512 bytes, sdf is 4096 bytes. mdadm -CRq /dev/md0 -l1 -n3 /dev/sd[de] missing --assume-clean # LBS is 512 cat /sys/block/md0/queue/logical_block_size # create partition md0p1 parted -s /dev/md0 mklabel gpt mkpart primary 1MiB 100% lsblk | grep md0p1 # LBS becomes 4096 after adding sdf mdadm --add -q /dev/md0 /dev/sdf cat /sys/block/md0/queue/logical_block_size # partition lost partprobe /dev/md0 lsblk | grep md0p1 ``` Simply restricting larger-LBS disks is inflexible. In some scenarios, only disks with 512 bytes LBS are available currently, but later, disks with 4KB LBS may be added to the array. Making LBS configurable is the best way to solve this scenario. After this patch, the raid will: - store LBS in disk metadata - add a read-write sysfs 'mdX/logical_block_size' Future mdadm should support setting LBS via metadata field during RAID creation and the new sysfs. Though the kernel allows runtime LBS changes, users should avoid modifying it after creating partitions or filesystems to prevent compatibility issues. Only 1.x metadata supports configurable LBS. 0.90 metadata inits all fields to default values at auto-detect. Supporting 0.90 would require more extensive changes and no such use case has been observed. Note that many RAID paths rely on PAGE_SIZE alignment, including for metadata I/O. A larger LBS than PAGE_SIZE will result in metadata read/write failures. So this config should be prevented. Link: https://lore.kernel.org/linux-raid/20251103125757.1405796-6-linan666@huaweicloud.com Signed-off-by: Li Nan Reviewed-by: Xiao Ni Signed-off-by: Yu Kuai

Merge tag 'docs-6.18' of git://git.lwn.net/linux

2025-10-04T00:16:13+00:00

Pull documentation updates from Jonathan Corbet: "It has been a relatively busy cycle in docsland, with changes all over: - Bring the kernel memory-model docs into the Sphinx build in the "literal include" mode. - Lots of build-infrastructure work, further cleaning up long-term kernel-doc technical debt. The sphinx-pre-install tool has been converted to Python and updated for current systems. - A new tool to detect when documents have been moved and generate HTML redirects; this can be used on kernel.org (or any other site hosting the rendered docs) to avoid breaking links. - Automated processing of the YAML files describing the netlink protocol. - A significant update of the maintainer's PGP guide. ... and a seemingly endless series of typo fixes, build-problem fixes, etc" * tag 'docs-6.18' of git://git.lwn.net/linux: (193 commits) Documentation/features: Update feature lists for 6.17-rc7 docs: remove cdomain.py Documentation/process: submitting-patches: fix typo in "were do" docs: dev-tools/lkmm: Fix typo of missing file extension Documentation: trace: histogram: Convert ftrace docs cross-reference Documentation: trace: histogram-design: Wrap introductory note in note:: directive Documentation: trace: historgram-design: Separate sched_waking histogram section heading and the following diagram Documentation: trace: histogram-design: Trim trailing vertices in diagram explanation text Documentation: trace: histogram: Fix histogram trigger subsection number order docs: driver-api: fix spelling of "buses". Documentation: fbcon: Use admonition directives Documentation: fbcon: Reindent 8th step of attach/detach/unload Documentation: fbcon: Add boot options and attach/detach/unload section headings docs: filesystems: sysfs: add remaining top level sysfs directory descriptions docs: filesystems: sysfs: clarify symlink destinations in dev and bus/devices descriptions docs: filesystems: sysfs: remove top level sysfs net directory docs: maintainer: Fix ambiguous subheading formatting docs: kdoc: a few more dump_typedef() tweaks docs: kdoc: remove redundant comment stripping in dump_typedef() docs: kdoc: remove some dead code in dump_typedef() ...

md/md-llbitmap: introduce new lockless bitmap

2025-09-06T09:27:51+00:00

Redundant data is used to enhance data fault tolerance, and the storage method for redundant data vary depending on the RAID levels. And it's important to maintain the consistency of redundant data. Bitmap is used to record which data blocks have been synchronized and which ones need to be resynchronized or recovered. Each bit in the bitmap represents a segment of data in the array. When a bit is set, it indicates that the multiple redundant copies of that data segment may not be consistent. Data synchronization can be performed based on the bitmap after power failure or readding a disk. If there is no bitmap, a full disk synchronization is required. Due to known performance issues with md-bitmap and the unreasonable implementations: - self-managed IO submitting like filemap_write_page(); - global spin_lock I have decided not to continue optimizing based on the current bitmap implementation, this new bitmap is invented without locking from IO fast path and can be used with fast disks. For designs and details, see the comments in drivers/md-llbitmap.c. Link: https://lore.kernel.org/linux-raid/20250829080426.1441678-12-yukuai1@huaweicloud.com Signed-off-by: Yu Kuai Reviewed-by: Li Nan

md/md-bitmap: delay registration of bitmap_ops until creating bitmap

2025-09-06T09:19:19+00:00

Currently bitmap_ops is registered while allocating mddev, this is fine when there is only one bitmap_ops. Delay setting bitmap_ops until creating bitmap, so that user can choose which bitmap to use before running the array. Link: https://lore.kernel.org/linux-raid/20250721171557.34587-7-yukuai@kernel.org Signed-off-by: Yu Kuai Reviewed-by: Hannes Reinecke Reviewed-by: Li Nan Reviewed-by: Xiao Ni

md/md-bitmap: add a new sysfs api bitmap_type

2025-09-06T09:19:04+00:00

The api will be used by mdadm to set bitmap_type while creating new array or assembling array, prepare to add a new bitmap. Currently available options are: cat /sys/block/md0/md/bitmap_type none [bitmap] Link: https://lore.kernel.org/linux-raid/20250829080426.1441678-6-yukuai1@huaweicloud.com Signed-off-by: Yu Kuai Reviewed-by: Hannes Reinecke Reviewed-by: Xiao Ni Reviewed-by: Li Nan

Fix typo in RAID arrays documentation

2025-08-29T22:29:18+00:00

Changed "write-throuth" to "write-through". Signed-off-by: Vivek Alurkar Reviewed-by: Randy Dunlap Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20250821051622.8341-2-primalkenja@gmail.com

Documentation: admin-guide: correct spelling

2023-02-02T18:04:42+00:00

Correct spelling problems for Documentation/admin-guide/ as reported by codespell. Signed-off-by: Randy Dunlap Reviewed-by: Mukesh Ojha Cc: Tejun Heo Cc: Zefan Li Cc: Johannes Weiner Cc: cgroups@vger.kernel.org Cc: Alasdair Kergon Cc: Mike Snitzer Cc: dm-devel@redhat.com Cc: Mauro Carvalho Chehab Cc: linux-media@vger.kernel.org Cc: linux-mm@kvack.org Link: https://lore.kernel.org/r/20230129231053.20863-2-rdunlap@infradead.org Signed-off-by: Jonathan Corbet

Documentation: fix multiple typos found in the admin-guide subdirectory

2020-12-08T17:27:56+00:00

Fix thirty five typos in dm-integrity.rst, dm-raid.rst, dm-zoned.rst, verity.rst, writecache.rst, tsx_async_abort.rst, md.rst, bttv.rst, dvb_references.rst, frontend-cardlist.rst, gspca-cardlist.rst, ipu3.rst, remote-controller.rst, mm/index.rst, numaperf.rst, userfaultfd.rst, module-signing.rst, imx-ddr.rst, intel-speed-select.rst, intel_pstate.rst, ramoops.rst, abi.rst, kernel.rst, vm.rst Signed-off-by: Andrew Klychkov Link: https://lore.kernel.org/r/20201204072848.GA49895@spblnx124.lan Signed-off-by: Jonathan Corbet

md: register new md sysfs file 'uuid' read-only

2020-08-03T06:03:51+00:00

Report the UUID of the MD array in the following format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx This is useful if you don't want to wait for udev to identify array. And it is also easy for script to monitor it with the format. Signed-off-by: Sebastian Parschauer [Guoqing: mention the change in md.rst] Signed-off-by: Guoqing Jiang Signed-off-by: Song Liu

Replace HTTP links with HTTPS ones: documentation

2020-06-08T15:30:19+00:00

Rationale: Reduces attack surface on kernel devs opening the links for MITM as HTTPS traffic is much harder to manipulate. Deterministic algorithm: For each file: For each line: If doesn't contain `\bxmlns\b`: For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`: If both the HTTP and HTTPS versions return 200 OK and serve the same content: Replace HTTP with HTTPS. Signed-off-by: Alexander A. Klimov Link: https://lore.kernel.org/r/20200526060544.25127-1-grandmaster@al2klimov.de Signed-off-by: Jonathan Corbet