Frankly, MD RAID is incomplete without checksum. Checksum is provided in Linux by dm-integrity.
Now, LVM2 can actually set up MD RAID with dm-integrity, however: * It doesn't expose all options. * It doesn't support specifying an MD journal for RAID4/5/6 to close the write hole. In addition, such an MD journal, if placed on a RAID1 of SSDs, can be used in `writeback` mode to speed up writes to the array. * It doesn't support dm-integrity without journal. If you are on RAID4/5/6, the MD journal (if you have one) should also cover incomplete writes at the integrity-level, thus there should not need to be a log in integrity level if you have one to cover the write hole at the MD level. * The LVM-RAID feature is relatively new, compared to `mdadm`-RAID. More guides and expertise are available on how to recover an `mdadm`-RAID failure versus an LVM-RAID failure. Thus, it would be nice to have a dm-integrity device mapper. However, some complications exist: * `integritysetup` defaults to tag size (checksum size) of 4 and using crc32c algorithm. However, you might prefer a stronger checksum by specifying a larger tag size and a different checksum algorithm such as "sha256". While `integritysetup` allows you to format a disk with your preferred checksum options, it only stores the tag size on the disk. Whenever you open the disk, ***you have to re-specify the algorithm*** in the `integritysetup open` command line. The same also applies to journal mode --- by default it will always open with full journal. Thus, I propose: * Add `arguments` field to `<mapped-device>` record type, default `'()`. This is a list, typically containing sequential key-value pairs. This field will be applied to the `open`, `close`, and `check` functions of the `<mapped-device-kind>` in addition to their existing arguments. * If the `arguments` list is empty, then existing `<mapped-device-kind>` will succeed. * Create an `integritysetup-static` package for use in `initrd`. * Create a new ``integrity-device-mapping` of type `<mapped-device-kind>`, which supports the following keywords in the `<mapped-device>` `arguments` list: * `#:algorithm` - a string (default `"crc32c"`) specifying the integrity algorithm. This should be the same as what you specified in the `integritysetup format` command in the `-I` option. * `#:journal` - one of the following strings: `"journal"` (default)` to indicate a full journal at the integrity level, `"bitmap"` to use a faster "dirty" bitmap, or `"none"` to disable journaling (for example if it already exists for all data at a higher layer). Thoughts?